[Gary HATFIELD devrait être mieux connu du public
français
- bien qu’il ait publié à ma connaissance un
article récent dans Les Etudes
Philosophiques en 2017, « L’attention chez Descartes : aspect
mental et aspect physiologique » - principalement à cause de son
commentaire suivi des Méditations
métaphysiques de Descartes qui a connu de nombreuses ré-éditions : et
de fait, ce Routledge Philosophy
Guidebook paru en 2002 (347 p.) contient un synopsis des arguments présents
dans les Six Méditations et n’a pas son équivalent en langue anglaise, pour sa
pertinence et sa clarté, dans la mesure où les Objections sont aussi intégrées au commentaire. Professeur de
philosophie moderne à l’Université de Pennsylvanie (Philadelphie), Gary
HATFIELD est surtout très respecté dans le monde académique pour son livre Perception and Cognition : Essays in
Philosophy of Psychology (2009), et pour : The Natural and the Normative : Theories of Spatial Perception from Kant to Helmholtz (1990),
devenu classique, encore qu’il ait
aussi traduit et présenté Les Prolégomènes
de Kant dans une version révisée en 2004. Il a également contribué à une
publication anthropologique remarquable avec Holly PITTMAN : Evolution of Mind, Brain, Culture, et
produit depuis 1977 près d’une centaine d’articles. HATFIELD jouit d’une grande
notoriété à travers son groupe de travail : le Visual Studies Program, qui connaît une audience internationale par
ses productions, ses dissertations et contacts divers avec S. Palmer et le
centre d’études sur la vision cognitive de Bielefeld. Dans ce même ordre
d’idées, le volume publié avec Sarah Allred chez Oxford, consacré aux
constances physiologiques et cognitives : Visual
Experience (Oxford UP, 2012) a justifié pleinement son invitation à
Aix-en-Provence lors de la soutenance de Ninuwé DESCAMPS le 15 décembre 2017. A
cette occasion, Gary HATFIELD a bien voulu nous communiquer une intervention
inédite qu’il a faite récemment, présentée ici sous forme de draft, dont le caractère formel illustre tout
l’esprit du SEMa, confortant le lien entre
l’histoire de la philosophie moderne et les études
plus récentes du groupe sur la perception et la géométrie de l’espace visuel,
en rapportavec la métaphysique réaliste. Nous l’en remercions vivement]
Gary Hatfield
Abstract. Classical constructivists such as Rock and
Hoffman contend that the processes of perception are intelligent and construct
perceptual experience by going beyond the stimulus information or by creating a
percept that deviates from the physical properties of the object. On these
terms, Gibson’s theory of perception is anti-constructivist. After reviewing
classical constructivism, this article maintains, first, that the phenomenology
of visual space shows a deviation from physical spatial properties, by being contracted
in depth, even under full-cue conditions, a fact that makes trouble for
Gibson’s version of direct realism. Second, independently of the first
argument, it contends that perception is pervasively constructed in the sense
that stimulus information must be transformed to yield perception. Accordingly,
perception is radically constructed in its very bones.
Keywords: construction in perception; visual space;
Gestalt psychology; James J. Gibson; Donald D. Hoffman; radical constructivism
Introduction
To say that experience is constructed can mean many things. One
prominent conception stems from Immanuel Kant, who developed an elaborate analysis
of how categorial concepts interact with sensory perception to construct the experience
of a world. This was a way of world-making
long before Nelson Goodman (1978) made that phrase famous. Although Kant held
that sensory perception is crucial in the construction of experience, he gave
greater attention to the categories and the experience of an objective world.
In contrast, this paper focuses on the construction of basic perceptual
experience, which, for what it’s worth, could be nonconceptual (presenting
basic properties like color and shape, independently of the concepts of color
and shape). It examines construction in spatial perception, especially vision, finding
that construction is pervasive. A radical constructivism is called for.
The notion that perceptual experience is a
construction arises from two main sources. First, the belief that perceptual
systems must cleverly manipulate information to produce perception is taken to
indicate that constructive processes underlie perception. For vision, this
means that the visual system creates the world of experience from ambiguous
stimulus information. Second, the fact that this constructed perceptual
experience sometimes, or perhaps even always, deviates from physical reality is
itself taken as a sign that the experience is constructed. The well-known
Necker cube illustrates both points (Fig. 1). It is two dimensional but we tend
to experience it in three dimensions. So the third dimension is added by
construction.
 |
Figure
1: The Necker cube. The drawing
is initially perceived as a spatial cube, with either the square containing the
upper-left corner as the front face, or the square containing the lower-right
corner. (Wait a few moments, and which cube is perceived will switch.) With
practice, the lines can be perceived as a flat hexagon, containing internal
triangles, squares, and other figures.
But, since the image on paper is flat and the experience is three dimensional, the experience deviates
from physical reality, suggesting that the experience include constructed
elements.
This paper first articulates these conceptions
of construction more fully. Subsequently, it argues that spatial perception is
deeply constructed, and should be so regarded even by Gibsonians. It offers a
notion of radical construction that does not require inferential elaboration of
stimulus information. This conception can be neutral about the mechanisms by
which the construction occurs. Construction can be pervasive, even if
perceptual processes are not clever.
1. Conceptions of
construction in perception
The first conception holds that perception must be cleverly
constructed out of impoverished information. Such construction is usually
understood to be a cognitive or inferential process (even if the perceptual
product is nonconceptual). A motivation for invoking construction is the view
that information for perception is skimpy or inadequate. To construct a
perception, an act of cognitive reconstruction
is needed, a kind of best guess about what is present.
Accordingly, as I look out upon a scene, the
basis for my perception is two impoverished images on my retinas (perhaps
supplemented by oculomotor sensations). The constructivist psychologist Irvin
Rock (1982, 1983) proposed that the basic processes which allow me to see the
shapes, sizes, and colors of things involve the intelligent application of
rules to this skimpy information, so as to yield a perceptual presentation of
the spatial and chromatic layout. (We leave aside here the harder problem of
classifying and identifying the kinds of things and the individuals in the
scene.) Rock allows that this reconstruction might be quite good, that it might
be completely accurate or veridical. However, skeptics charge that if
perception is a reconstruction from poor information, it is subject to mistakes
and distortions in the same way as other reconstructive processes are fallible
and prone to error. Memory is one such reconstructive process, as psychologists
understand it (e.g., Neisser and Libby 2000). As regards vision, the danger is that
constructive perception might be a mere fabrication or concoction.
This first conception is motivated by the
discrepancy between the impoverished two-dimensional retinal image and three-dimensional
perceptual experience, so that construction makes up the difference. The second
main conception works the other way around, starting from a mismatch between
perception and the external physical scene and concluding from there that
perception is a construction in the first sense. Donald Hoffman (1998) promotes
this line. He emphasizes mismatches such as those described by the Gestalt
principles of organization. These include figure-ground relations, in which
figures become more salient than ground even though, physically, they have the
same reality as surfaces, as with the black lines and white surface of the Necker-cube
line drawing. They also include cases in which the same physical shape takes on
different organizations in the absence of any intrinsic change, as when the
cube shifts orientation (a “Gestalt switch”). The perceived change in the
orientation of the cube is a subjective addition with no corresponding physical
reality, yielding two different three-dimensional misperceptions of the same
group of two-dimensional black lines. Hoffman concludes that, because
perception is constructed in these respects, it might be a mere construction
more generally, that is, a fabrication or concoction (1998, ch. 8).
Traditionally, the position opposed to
constructivism in the psychology of perception is Gibsonian direct realism. James
J. Gibson (1950, 1966, 1979) argued that rich information is available to
visual systems in ordinary conditions of viewing, with both eyes open, good
lighting, and a mobile perceiver. This information is sufficient to specify the
spatial layout. There is no need for “clever” or “intelligent” reconstructive
processes. We perceive the world veridically simply by picking up the rich
information. (On Gibsonian theory versus constructivism, see Norman 2001.)
A philosophical counterpart to Gibson’s direct
realism is the naïve direct realism now popular in parts of England,
California, and New Jersey. On this view, no construction is needed because the
world with its physical properties is directly touched by the conscious mind,
through a relation of unmediated acquaintance. I have elsewhere detailed the
shortcomings of this form of nonconstructive theory (Hatfield 2016), and so I put
it aside to focus on the ideas of Rock, Hoffman, Gibson, and, as needed, the
Gestalt psychologists, especially Kurt Koffka (1935).
To recapitulate, the first two authors hold that
perception is a construction but disagree on whether it is therefore suspect as
regards veridicality. Rock (1981, p.502; 1983, p.302) leaves the matter open,
holding that perceptual constructions may be veridical or not. Hoffman (1998) contends
that because perception is a construction that deviates from physical reality, as
in Gestalt effects, it is suspect. It might be a deeply faulty reconstruction
of what is really there. Gibson (1966, 1979) argues that because visual
information, when properly analyzed, is able to specify the physical properties
of the scene, there is no need for construction; usually, perception veridically
presents us with the physical properties of a mind-independent reality.
Hoffman and Gibson agree that any deviation of
phenomenal experience from the external physical environment is evidence of
construction (even if Gibson holds that such deviation is aberrant). We can
call this shared conception of construction PDE:
PDE
(Phenomenal deviation from physical environment) The deviation of phenomenal experience from the external physical
environment indicates perceptual construction.
The Gestalt psychologists, whom Hoffman and Gibson each invoke, agree
with PDE in principle, without using the terminology of “construction.” That
is, they recognize that the experienced behavioral environment deviates from
the physical or geographical environment due to perceptual processes (Koffka
1935, pp.27–41). Hoffman and Gibson both think of such deviation as a kind of
misperception. Here I disagree, as would the Gestaltists.
Because I disagree, I want to draw a different
map of the relations among these positions and of the implications that follow
from accepting that perception is constructive. To do this, I must first broaden
the notion of construction. I want to include all cases in which the visual
system must transform its input in
order to produce perception. I thus endorse CT:
CT (Construction
as transformation) Any
aspect of perception that differs from proximal stimulation as received at the
sense organs is to be deemed a transformation and hence a construction.
CT broadens the notion of construction to include as a
transformation and hence a construction any instance in which what is perceived
regularly differs from the energy distributions received by the sense organs. Rock
agrees already. The Gestaltists (Koffka 1935, pp.129–41; Köhler 1947, pp.132–3)
happily recognize that perceptual
processes in vision respond to the two-dimensional stimulus mosaic by producing
an experience in three dimensions, which presents the world under a specific
aspect (including organizational features such as figure-ground). Gibson might
say that he is not involved in any kind of perceptual construction, except in
deviant cases.
CT may seem so broad as to be weak. My job is to
show that, in fact, under this broad notion, striking but usually unnoticed
instances of construction reveal themselves. I will show that such
transformations and constructions must occur even for Gibson. Indeed, it is
only from the implausible perspective of naïve realism that perception just
copies, or directly encompasses, physical things. Any description of perceptual
processes that pays attention to the characteristics of optical stimulation
will note that what the eyes receive, no matter how rich it may be in information,
does not copy the world and so must be transformed to yield perception.
I will argue further that perceptual deviations
in presenting external physical properties need not be characterized as
misperceptions, or even as non-veridical. Here, the standards of veridicality
track presentations of the environment in a way that is adequate for the
guidance of action:
AA
(Aspect for action)
Perception presents the environment under an aspect in a manner suitable for
action guidance; deviation from mind-independent physical properties need not
be a “mistake.”
I will offer phenomenal grounds for believing that ordinary
spatial perception does not match the physical scene, but presents it under an
aspect. To follow the Gestalt psychologists for a moment, there is a difference
between a phenomenally described behavioral environment and the geographic or
physical environment that phenomenal experience presents (Koffka 1935,
pp.27–31). The behavioral environment, although not a literal copy of the
physical environment, nonetheless presents that environment in a way that can
be relied upon for acting within it.
Consequently, perception is more deeply
constructed than the usual notions of constructivism tell us. Perception
includes a phenomenal construction that differs from a bare representation of
mind-independent reality, which need not be a bad thing. Indeed, for the
purpose of guiding action, a subject-dependent, environment-tracking phenomenal
construction may be just what is needed.
2. Constructivism, Gibson, and Gestalt on phenomenal
experience
Gibson
(1966, chs. 10, 11, 14; 1979, ch. 14) considered the accepted theory of visual
perception, the traditional constructivist account, to consist of these key
points: the stimulus for spatial vision is impoverished, failing to specify the
third dimension; this stimulus produces “sensations” that mirror the proximal
stimulus (the retinal image in the case of vision); in order to compensate,
computations or inferences based on memory or past experience are required,
which yield a constructed perception that may or may not be veridical.
The constructivist view can be illustrated by considering
these diagrams of the size-distance invariance hypothesis (SDIH). The physical
relation between the height of objects, their distance, and their visual angle
(which correlates directly with their retinal projections) is shown in Figure 2.
Equally tall objects at different distances produce retinal projections that
diminish as the distance of the object increases (Fig. 2a). A tall object (Fig.
2b, A) and shorter near one (C) can produced the same visual angle
(retinal projection). But how are these perceived? Rock held that perception,
at least for near objects, often achieves full phenomenal size constancy (1975,
pp.31–2; 1982, pp.528, 532). The perceived size (in this case, height) depends
on both visual angle (which is constant for an object at a given physical distance)
and perceived distance. If the distance is accurately perceived, objects are
perceived at their true locations with their actual sizes (A and C), a result known
as size constancy. If the distance is
under-perceived or over-perceived, the objects are seen as nearer and smaller (at
B and E) or farther away and larger (A
perceived as at D), respectively
called under-constancy and over-constancy.
 |
|
Figure
2: Part (a) shows
poles of equal height at different distances. The poles farther away produce
corresponding smaller visual angles (retinal images). If perceived distance
matches physical distance, then, in accordance with the SDIH, perceived size
matches physical size. Part (b) illustrates the SDIH for two objects, A and C, that are at different distances but project the same visual
angle. Depending on the perceived distance of the objects, the perceived size
varies.
|
To replace the constructivist picture, Gibson proposed
that the stimulus for vision carries rich information that unequivocally specifies
the spatial layout. This information is picked up by the visual system to yield
a direct perception of the layout with its objective properties, (allegedly) obviating
the need for computations or inferences. We do not, in normal veridical
perception, have mediating perceptual experiences, whether of a proximal
“sensation” or of the objective visual scene. Under impoverished stimulus
conditions, size and shape constancy may indeed break down so as to reveal,
according to constructivism, the true elements of perception: more distant
objects produce smaller sizes in sensation, pennies seen at a slant produce
elliptical sensations. But, according to Gibson, far from being fundamental,
these aberrant sensations play no role in the ecologically normal situation of
rich stimulation, in which the scene is perceived as it is (1966, chs. 10, 12;
1979, chs. 4, 14).
Gibson often wrote as if impoverished proximal sensations
and direct perception of the physical layout were the only choices (1950, ch.
3; 1966, ch. 14). He contended that, in speaking of things looking small in the
distance or of a penny at a slant looking elliptical, one is forcing proximal
sensations into experience, either through impoverished viewing conditions or
by adopting a special attitude, called the pictorial
attitude, which yields an experience corresponding to a perspective
projection of the scene into a two-dimensional plane (1950, p.27; 1966, pp.235–8,
306–7). Without impoverished conditions or the pictorial attitude, things
should not look small in the distance under full-information or full-cue
conditions. Indeed, Gibson acknowledged that if full-cue perception did not
conform to the “objective facts” (1966, pp.6, 306) of the environment, his
theory would be in trouble (1966, p.306; 1979, pp.166–7). Problematic examples would
include “incomplete perceptual constancy” (1966, p.306; 1979, p.160), as when a
coin looks elliptical or railway tracks converge phenomenally.
If incomplete constancy was found in full-cue cases, Gibson
contended either that the described result reflects poor phenomenology, or that
taking the pictorial attitude creates sensations that intrude upon experience.
He countered the poor phenomenology by saying that the penny looks like a
circle at a slant so that, unless viewed at an extreme angle, it looks like a
circle. I find this response compelling. He responded to the claim that things
look small in the distance by saying that, in fact, they don’t. He cited an
experiment with stakes in an open landscape in which average responses of full
constancy were achieved even at a distance of 700m (1950, pp.174–87; 1979, p.160).
If this means that, under ordinary perceptual conditions, there is no
phenomenal diminution at distances of a 200m – or 30m, or 7m – I am
incredulous. I don’t believe it. I am not saying that, to an adult observer,
things look as if they were diminished in physical size in the distance. Nor am
I denying that one can alter the experience of size by taking the pictorial
attitude. But I am asserting that, in normal perception, without the pictorial
attitude, things are diminished phenomenally in the distance (as Rock 1982,
p.533, allows).
Let us return to the phenomenological point anon. Gibson considered
the Gestalt tradition to be distinct from standard constructivism (1950,
pp.22–3; 1966, pp.266–7). Koffka’s Principles
of Gestalt Psychology laid out a theory of perception which accepted the
impoverishment of the stimulus with respect to perceptual experience but
rejected the idea that perceptual experience results from intelligent
operations based on proximal sensations (1935, pp.85–8). The impoverished
stimulus can yield a presentation of a spatial and chromatic world because
brain processes operate dynamically to produce organized perception, tending in
the direction of the constancies of shape, size, and color. Organization
includes figure-ground relations (including enhanced contrast at edges),
grouping by proximity or similarity, a tendency toward symmetry and simplicity,
and so on. (On the relations among Gibson, the Gestalt psychologists, and Rockian
constructivism, see Epstein 1994.)
The Gestalt psychologists accepted a distinction between
physical objects and the perceptual experience of those objects. The physical
objects are not directly present to consciousness, but our perceptual
experience “mediates” contact with the physical environment. Koffka called the
world of immediate experience the behavioral
environment, as opposed to the physical or geographic environment. In
a famous example, a horseman on Lake Constance rides over solid ground in his
behavioral environment (he perceives the flat snow-covered expanse as a
snow-covered meadow), but in his geographical environment he in fact rides over
the thin ice of the lake, which happens to bear the weight (1935, pp.27–8).
Koffka describes the phenomenally present behavioral environment as achieving
“the mediation between geographical environment and behaviour” (1935, p.36).
Although one might take this behavioral environment to be
a kind of sense datum, I don’t read Koffka that way. Rather, the behavioral environment
is a presentation of the geographical environment under an aspect. It presents
the world phenomenally, in a subjectively conditioned way. Further, the Gestaltists
did not believe that in order to be correct perception had to present only
objective, mind-independent physical structures. Perception presents the world
as having figure-ground organization, enhanced edges, groupings, and the like.
The Gestaltists did not consider these departures from a neutral physical
description to be illusions or mistakes. As illustrated in this photograph
(Fig. 3), figure-ground organization can enhance object boundaries and help to sort
out overlapping structures in space.
 |
Figure
3: Figure-ground
organization segregates the various items as phenomenal units, including
presentation of surfaces as continuing underneath smaller units, and
segregation of various smaller units from one another.
I believe that Gibson did consider these departures from
physics as mistakes. His ecological psychology took into account “ecological”
facts such as the scale of the environment in relation to the organism, the
placement of the organism in relation to a scene, standing features of
illumination and of surfaces, and the relation of the animal to media such as
air, land, or water. He said that these factors have a “subjective” element, by
which he did not a mean mind-dependent aspect, but rather the physical relation
of the subject to the scene, including the subject’s physical size in relation
to the physical sizes of things. He retained the notion that “objective” means
what is determined by ordinary physical properties (1966, pp.6, 306; 1979, pp.8–9,
126, 129, ch. 9). Thus he did not escape, as he might have, the naïve realist
preference for an “objective” physical world that perception reveals (albeit at
an organismic scale).
Now we can return to size perception and the
phenomenology of things looking small in the distance. Recall that Gibson
believed that this phenomenology is artificially produced, by taking a pictorial
attitude, so as to experience a two-dimensional perspective image of the scene.
Our attitude produces an experience of intermediate sizes and shapes (as in a
perspective rendering). But, he claims, with full-information and no attitude,
we should perceive shapes as and where they are with their true sizes. He held
that, in the normal case, there is information to specify the true sizes of
things. Examples include the fact that an object on the ground covers the same
amount of (homogenous) ground texture independently of the distance. This
invariant relation between ground texture and size provides the information for
size constancy (Gibson 1979, p.163). Or, for a person standing and looking at a
row of light poles of equal height, poles both near and far are cut by the
horizon line at the same proportional location; given that eye-height is known,
information for the physical heights of the poles is present through the
proportional relations (Gibson 1979, p.165). Gibson claimed that such
higher-order ratios in the stimulus array directly specify the “objective,”
that is, physical, layout (1979, pp.126, 129, ch. 9), thereby avoiding any need
for subjectively conditioned representations.
There are things to challenge conceptually in Gibson’s
claim. For instance, one might wonder why the receipt at the visual system of
information sufficient to specify the layout should produce a direct unmediated
acquaintance with objects, as posited (problematically) by naïve direct
realism. But I prefer to mount a phenomenological challenge. I believe that
Gibson has used binary thinking in attributing the phenomenology of
intermediate constancy to intruding sensations. On the contrary,
phenomenological reflection, also supported by experimental evidence, suggests
that intermediate results are quite normal.
Let’s consider the notion of size constancy and things
seeming smaller in the distance. Koffka (1935, p.229) held that the
size-distance invariance hypothesis (not his term) covers this case. The SDIH
doesn’t itself specify what size something will appear to have, but it says
that, holding visual angle constant, the perceived size of an object directly varies
with its perceived distance (Fig. 2b). If an object is perceived as being at
its true physical distance, then it should be perceived with its true size; if
it is perceived as nearer, it will be phenomenally smaller.
The perception of railway tracks extending into the
distance, or of a long, straight hallway in a building, offer counter-instances
to Gibson’s phenomenology. I perceive railway tracks as converging (Fig. 4).
This convergence is not merely, as Gibson supposes, a convergence in perspective.
If it were, I would experience the tracks as in a two-dimensional perspective
projection, which would mean – for the usual perspective plane perpendicular to
the line of sight – that they would appear perpendicular to the ground and
would project into an upright, rather truncated triangle (Fig. 4, right). But
my experience, looking down the tracks, is of them receding into the distance
(in the third dimension). They converge, but they do so as they extend toward
the horizon. And, indeed, there is good evidence that, in normal perception,
perceived distance falls short of physical distance, the more so the farther
away things are (Hillebrand 1902; Blumenfeld 1903; Wagner 2006, chs. 6–7; see
also Hatfield 2003, 2016).
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|
Figure
4: Railway tracks perceived as converging into the distance. The photograph
(left) gives a sense of depth; on real tracks, the sense of depth and distance
is even more salient. If our experience matched a perspective projection, it
would be of an upright triangle (right).
|
In order to understand the regularity of this
phenomenology, consider Figure 5, a drawing from Aage Slomann (1968). The
drawing shows a rectangular space, say, a hallway, with a physically flat floor
Ff running from observer P1’s
feet (at d) to staff bc. Slomann reports that we do not
experience the floor as “flat” in the sense of forming a ninety-degree angle
with the observer’s body (or being perpendicular to gravity), but that the floor
phenomenally rises. I agree. And if the floor rises while the directions to
locations on the physical floor remain the same (that is, while we continue to
perceive directions veridically, which in fact we do), then distance must be
under-perceived. For example, location c
appears in the direction given by the line ac,
but because it is seen in relation to the floor, it appears in location f, at the shorter distance af. Taking this condition of the ground
phenomenally rising to be general, then, in accordance with the SDIH, objects
at a distance will appear closer and smaller, as physical staff bc appears at phenomenal location gf. The space is contracted in the
in-depth dimension (along lines of sight). There is, in fact, no optical reason
why the ground couldn’t appear flat and things appear where they are at their
true sizes (e.g., staff bc at
location bc), but that would be quite
strange for us: it would mean that the train tracks don’t appear to converge,
or that buildings a kilometer away aren’t phenomenally of less extent than the
same building 20m away.
 |
|
Figure
5: An illustration of
the effects on phenomenal visual space if distance is under-perceived. For
observer P1 (ad), the ground
(dc) appears to rise (de), and objects appear closer and
smaller (bc appears at gf). From Slomann
(1968, Fig. 1).
|
It bears repeating that this diminution or contraction,
although related to perspective, is not the same thing as linear perspective,
which is the projection of the three-dimensional world onto a two-dimensional
plane. This contracted space may be viewed as a phenomenal presentation of the
physical or geographical environment under an aspect in which distance
contracts in a regular manner. In this visual space, much useful information is
phenomenally available: phenomenal direction is congruent with physical
direction, objects retain an invariant proportion to their surrounds across
different distances and phenomenal sizes, next-to-ness relations on surfaces
are preserved, as are ordinal relations along the ground plane, and so on (see
Hatfield 2012, 2016). Phenomenal experiences of these relations satisfy a norm
for perception in accordance with AA, that perception presents the environment
under an aspect suitable for action guidance. Such norms include appearing in
the right direction, retaining proportional size, and so on. Deviation from perceiver-independent
physical properties need not be a “mistake.” Indeed, it is presumably better that
things 100m away do not appear with the same phenomenal size as when they are
near at hand.
These findings challenge Gibson’s phenomenology. Size
constancy is intermediate (see also Daoust 2017). Shape, at the scale of a
hallway, is also affected (floors in a long rectangular hallway appear as
elongated trapezoids). As Gibson realized, this favors phenomenal mediation. If
the object is not itself directly present in experience, but is presented in
manner that is subjectively conditioned, then the natural place to find the
object as presented under an aspect is in subjectively conditioned phenomenal
experience. The Gestaltists and Gibson agree on this (even if Gibson tries to
avoid the conclusion through his phenomenological argument). They accept an
age-old logic for drawing a distinction between appearance and reality: that
properties as present in experience deviate from mind-independent physical
properties. This need not, by the way, commit one to appearances as sense data.
Appearances can be conceived as presenting the physical world under an aspect
(Hatfield 2016).
Contrary to Gibson’s direct realism, we don’t perceive
the world just-as-it-is physically. This raises the following question about
size: Even if Gibson is right that in ecologically normal situations
information sufficient to specify physical size and distance is present, why
should the physical value be the target of perception? What is wrong with
contracted space, if it is ecologically adequate, and perhaps preferable, for
guiding action? Size perception can be about relations, directions, and
proportions, presented perceptually in a way that guides action. It needn’t be
about mind-independent sizes and distances, although these can be ascertained
from the layout as perceived, through known operations of measurement or
estimation.
If we accept the phenomenal intermediacy of size
perception, then we should accept that perception is a construction, in accordance
with PDE (phenomenal deviation from the physical environment):
PDE: The deviation of phenomenal experience from the
external physical environment indicates perceptual construction.
The Gestaltists might embrace this point and see it as an
extension of their notion that perceptual processes produce phenomenal
organization that is beneficial. Rock and Hoffman already have accepted this
conclusion. Gibson wouldn’t want to accept phenomenal deviation in normal cases,
but that’s too bad for him. In fact, even worse is in store.
3. Perception as radically constructed
Let us now consider perception as constructed according to CT,
construction as transformation:
CT: Any aspect of perception that differs from
proximal stimulation as received at the sense organs is to be deemed a
transformation and hence a construction.
There are obvious instances of such transformations, as in Rock’s
conception that ambiguous two-dimensional stimulus information must be
transformed by intelligent perceptual processes to yield the experience of
surfaces in three dimensions. Hoffman would accept that construction in perception
involves somehow transforming what is contained in retinal images into
organized percepts. The Gestaltists would accept something similar, while of
course not conceiving the processes, with Rock and Hoffman, as clever or
intelligent. Gibson would allow that such transformation occurs in the case of
illusions. Otherwise, he would not want to accept that construction occurs in
everyday full-cue perception of a three-dimensional world. My first task is to
show that even leaving aside the phenomenal criterion for construction from the
previous section (PDE), that is, putting aside for now my phenomenological
argument, Gibson and his followers should accept this broader notion of
construction in perception.
Let us continue to grant Gibsonian claims about rich
information. There is still a need for some mechanism or process to transform
stimulus information into perception of the visual world. The information
available to the visual system does not copy the world, rather it specifies it
in relation to a system that is attuned to, and resonates with, the available
information.
An example may help. Gibsonians have successfully
analyzed optic flow patterns that produce perception of the motion of the
observer through the environment (see Warren 2008). When an observer moves forward
in a static environment with normal optical texture, that motion produces a
flow pattern of outward radial expansion at each eye (Fig. 6). This information
results in an experience of forward motion through the environment. There is,
however, an obvious difference between expansion within the optical array,
which can be represented in two dimensions and is sampled by the two-dimensional
surface of the retina, and the visual phenomenal experience of moving forward
in depth. Gibson recognized this, and offered a division of labor to handle it.
As a psychologist, he was working at the level of perceptual systems and the
analysis of stimulus variables. If he found a psychophysical relation between
optical expansion and perception of forward motion, he then said that the
perceptual system detects the information that specifies the motion. If pressed
on how this occurs, he allowed that receptors respond to light energy, but
maintained that it was not his job to say how the receptors and visual nervous
system integrate the patterns of stimulation. He was ready to move on after
finding complex stimulus information that specifies the physical environment (1950,
p.viii; 1966, pp.2–5, 167; 1979, pp.53, 251, 263).
 |
|
Figure 6: An
optical flow pattern produced by the forward motion of an observer through a
stationary setting with normal optical texture. Optical features expand from
the point of fixation in the scene. From Palmer (1999, p.227).
|
Nonetheless, Gibson allowed that neuroscientists might ask
how receptor systems respond to and integrate the information in optic flow
(1979, p.251). Neuroscientists answered by seeking neural mechanisms for detecting
optic flow. An early effort was van de Grind (1988). He proposed motion-detecting
neural mechanisms organized in a ring (see also Duffy 2004). For global optic
flow, the detectors would be set in concentric rings centered on the fovea. Motion
detectors are velocity and direction specific. These detectors would be
oriented so as to respond to local motion of optical features moving outward on
radial lines and crossing the concentric rings perpendicularly. Van de Grind
suggested a similar mechanism for more localized optical expansions with the
information that an object, such as a soccer ball, is approaching the
perceiver’s head. These two mechanisms take as input local or global optical
expansion and produce the perceptual experience either of a looming object
moving toward the perceiver or of the perceiver moving forward. By CT, these
are instances of construction as transformation.
 |
|
Figure 7: Reflection of light from external points
V, X, Y into the eye. Proper
refraction of the light rays focuses the light on to points R, S,
T. Originally published in Descartes
(1637, p.36). Reproduced
from Descartes (1692, p.58).
|
A Gibsonian might object that there is no construction
because there need be no underlying “intelligent” or hyper-intellectualized
processes. But notice that I haven’t characterized any processes as symbolic,
conceptual, inferential, or the like, the usual suite of words associated with Rockian
construction. This is because I have sought to render the criterion for
construction neutral between Rock and Gibson. The point is to define construction
as a perceptual process, however conceived, in which perception results from a
transformation of stimulus values. We clearly have a transformation in the case
of optical flow patterns, which are not themselves three dimensional but yield
the perception of motions in three dimensions (observer motion or ball motion).
This sort of construction is needed even if we accept Gibson’s rich
information. In accordance with neutrality, any “computations” involved might
be effected by nonconceptual connectionist nets or by Rockian intelligent
inferences (see Hatfield 1990). CT doesn’t specify. Accordingly, cognitive
constructivism, as with Rock or Hoffman, becomes but one subspecies of construction
as transformation (CT).
But now I want to convince you that perception is even
more radically constructed – that it is constructed in its very bones. Let us begin
with a very basic aspect of vision: that we see in straight lines. This has
been theorized since ancient and medieval times, in the optical writings of
Euclid, Ptolemy, Ibn al-Haytham, and Witelo (see Lindberg 1976). The precise
geometry by which light reaches the retina was discovered by Kepler and
illustrated by Descartes in his widely known writings on optics and visual
physiology, the Dioptrics (1637) and
the Treatise on Man (1664). This
finding is illustrated here in Figure 7, Descartes’ diagram of 1637. The
physical path of light is shown from illuminated points V, X,
and Y to retinal locations R, S,
and T.
Notice that pencils of
light come from each point (or small area) on the object VY. These pencils bathe the entire front of the eye, but, due to
the refractive power of the cornea (the clear cover at the front of the eye)
and the lens, the rays are focused onto the retina in small regions at R, S,
and T (with other points on VY projecting to all points in between).
So far, we have the physical path of the light to the
retina. A natural assumption, made by Descartes and Kepler and generally affirmed
by subsequent theorists, assumes that we see points of the object in the
direction in which they lie, projecting outward from the stimulation of the retina
(Hershenson 1999, pp.12–15). Thus, we should experience point Y as in the direction projected back
from T, and points V and X along their own lines of projection. In accordance with the deeply
held assumption that we see in straight lines directed toward the illuminated
regions that send light to the retina, we readily accept that this is how the eye
works. If we then take it that these visual directions form the bones of our
experience in the three dimensional world, we can use this ray geometry to
understand the perception of size and shape. So, accepting that we see the
various points of object VY in the direction
that they lie, we can see the shape and distance of VY by perceiving the distances to these points.
Here I want to ask a question so basic that it may seem
ludicrous. Why should we see the points V,
X, Y in the directions in which they lie? This is the same as asking
why retinal stimulations at R, S, T
should produce the experience of a small region of light localized in directions
toward V, X, Y. It can’t be simply a
matter of the direction of the light. If it were only that, why wouldn’t we
experience all the directions the light takes in approaching each retinal point,
as represented in the pencil of rays converging on point R, point S, and point T? In such a case, we might project back
from each point along a cone of rays. But we don’t. If, however, the actual
physical direction of the impinging light is not sufficient for predicting
visual direction (by tracing back), we are free to imagine various relations
between the stimulation of retinal points and experienced direction. So, why
not projection in other ways (Fig. 8)?
Clearly, our intuition is that the potential phenomenal
directions for stimulation of R as shown
in Figure 8 would not produce a good result. For well-functioning vision, we
should see the light in the direction from which it comes by tracing a single
line back through the center of the eye (or the center of focus), such as lines
from R to V, S to X, and T to Y. But notice, this
is already a transformation.
 |
|
Fig 8: There is no logical (or purely physical)
reason why stimulation at R shouldn’t
result in an experience localized in the direction of the arrow on the right,
or of the arrow on the left, or any other direction.
|
The light hitting the retina does not by itself carry the information of
the direction from which it came. It is only because of the peculiar
psychophysiology of our visual system that the eye experiences a luminous point
as lying in the (central) direction from which the light came. The point of
light on the retina is not a copy of the direction, but merely a physical
result of light coming from a direction. Hence, we have here a transformation
from the light stimulating the retina to the experience of a visual direction.
According to CT, we have a construction.
 |
|
Figure 9: Differing focal lengths when the eye is
accommodated
near (B0) or far ( B1). From Helmholtz (1867,
p.584).
|
Looking still
more closely, we find that this construction is more complicated than
advertised. In fact, the optics of the eye changes for near and far vision.
This means that the paths taken by light in the eye differ as a result of these
changes. If we assume that visual direction from the retina is preserved, the
experienced visual direction has first one, then another relation to a central
path of light in the eye. The lens in the eye must accommodate, or change its
shape, to produce an image in focus for objects at different distances (say, 1m
and 2m). Figure 9 shows the focal lengths in the eye corresponding to the two
arrows on the left. B1 is
the focal length for the arrow at the far distance, B0 for the closer arrow. In order to see them both with
the same angle, as is expected on the assumption that the retinal image of the
arrow, FG, is the same in the two
cases, there must be
differing
constructions of visual direction in relation to the central physical path
taken by the light within the eye as accommodated for the near and far arrows.
But things get worse, at least for deniers of
construction. I have so far been following visual direction for a single eye.
But human vision is normally carried out with both eyes, as in Figure 10. The
two eyes are directed toward a focal point (fixation point F).
 |
|
Figure 10:
Binocular vision, showing points in the field of view as projected into real
eyes LE and RE. Phenomenal or perceived visual directions proceed from the
Cyclopean (virtual) eye, located between the two real eyes. From Hershenson
(1999, p.22).
|
References
Blumenfeld, Walter (1913).
Untersuchungen über die scheinbare Grösse im Sehraume. Zeitschrift für Psychologie und Physiologie der Sinnesorgane 65: 241–404.
Daoust, Louise. 2017. Seeing Things As
We Do: Ecological Psychology and the Normativity of Visual Perception. Ph.D.
Dissertation. University of Pennsylvania.
Descartes, René. 1637. La Dioptrique.
Maire. Trans: Discourse on Method, Optics, Geometry, and Meteorology,
trans. Paul J. Olscamp. Bobbs-Merrill, 1965.
———. 1664. L’Homme. Angot. Trans.: Treatise of Man, trans. Thomas S. Hall.
Harvard University Press, 1972.
———. 1692. Specimina Philosophiae: seu Dissertatio de Methodo, Dioptrice, et
Meteora. Knoch.
Duffy, Charles J. 2004. The cortical analysis
of optic flow. In: Leo M. Chalupa and John Simon Werner (eds) The Visual
Neurosciences, vol 2, pp.1260–83. The MIT Press.
Epstein, William. 1994. “Why do things
look as they do?”: What Koffka might have said to Gibson, Marr, and Rock. In Stefano Poggi (ed) Gestalt Psychology: its Origins, Foundations
and Influence, pp.175–89. Olschki.
Gibson, James. J. 1950. The
Perception of the Visual World. Houghton Mifflin.
———. 1966. The Senses Considered as Perceptual Systems. Houghton Mifflin.
———. 1979. The Ecological Approach to
Visual Perception. Houghton Mifflin.
Goodman, Nelson. 1978. Ways of Worldmaking. Hackett Publishing.
Hatfield, Gary. 1990. Gibsonian
representations and connectionist symbol-processing: Prospects for unification.
Psychological Research 52:
243–52.
———. 2003. Representation and
constraints: The inverse problem and the structure of visual space. Acta
Psychologica 114: 355–78.
———. 2012. Phenomenal and cognitive
factors in spatial perception. In Gary Hatfield and Sarah Allred (eds) Visual
Experience, pp.35–62. Oxford University Press.
———. 2016. Perceiving as having
subjectively conditioned appearances. Philosophical Topics 44(2): 149–78.
Helmholtz, Hermann von. 1867. Handbuch
der physiologischen Optik. Voss.
Hershenson, Maurice. 1999. Visual
Space Perception. The MIT Press.
Hillebrand, Franz. 1902. Theorie der
scheinbaren Grösse beim binokularen Sehen. Denkschrift der
Kaiserlichen Akademie der Wissenschaften Wien,
Mathematisch-Naturwissenschaftliche Classe 72: 255–307.
Hoffman, Donald D. 1998. Visual Intelligence: How We Create What We
See. W. W. Norton.
Julesz, Bela. 1971. Foundations of Cyclopean Perception. University of Chicago Press.
Koffka, Kurt. 1935. Principles of Gestalt
Psychology. Harcourt, Brace and Company.
Köhler, Wolfgang. 1947. Gestalt Psychology: An Introduction to New
Concepts in Modern Psychology. Liveright.
Lindberg, David C. 1976. Theories of
Vision from al-Kindi to Kepler. University of Chicago Press.
Neisser, Ulric, and Lisa K. Libby. 2000.
Remembering life experiences. In: Endel Tulving; Fergus I. M.
Craik (eds) The Oxford Handbook of Memory,
pp.315–32. Oxford University Press.
Norman, Joel. 2001. Two visual
systems and two theories of perception: An attempt to reconcile the constructivist
and ecological approaches. Behavioral and
Brain Sciences 25(1): 73–96.
Rock, Irvin. 1975. Introduction to
Perception. Macmillan.
———. 1982. Inference in perception. In:
Peter D. Asquith; Thomas Nickles (eds) PSA:
Proceedings of the Biennial Meeting of the Philosophy of Science Association,
Volume Two: Symposia and Invited Papers, pp.525–40. Philosophy of Science
Association.
———. 1983. The Logic of Perception.
The MIT Press.
Slomann, Aage. 1968. Perception of size:
Some remarks on size as a primary quality and “size constancy.” Inquiry 11:101–13.
Palmer, Stephen E. 1999. Vision
Science: Photons to Phenomenology. The MIT Press.
van de Grind, W. A. 1988. The possible
structure and role of neuronal smart mechanisms in vision. Cognitive Systems
2(2): 163–80.
Wagner, Mark. 2006. Geometries of
Visual Space. Erlbaum.
Warren, William H. 2008. Optic flow. In:
Allan I. Basbaum, Akimichi Kaneko, Gordon M. Shepherd and Gerald Westheimer
(eds) The Senses: A Comprehensive Reference,
vol 2, Vision II (ed) Thomas D.
Albright and Richard Masland, pp.219–30. Academic Press.
Gary
Hatfield
Department
of Philosophy
University of Pennsylvania
Philadelphia, Pennsylvania
hatfield@sas.upenn.edu
[1]
Paper given at the Xth Principia International Symposium: The Construction of
Experience (Florianopolis, Brazil, August, 2017). In preparation for the
journal Principia (in a translation
into Portuguese).
