1
Computational properties of interhemispheric communication
between abstract and specific visual-form subsystems
David R. Andersen & Chad J. Marsolek
Elliott Hall, N218, 75 East River Rd, Minneapolis, MN 55455,
E-mail: dandrese@levels.psych.umn.edu,
Tel. 612-626-1546
The neural processing subsystems underlying vision are only weakly modular.
We investigated implications of this neural architecture for visual-form
recognition subsystems and interhemispheric communication between them. In
a behavioral experiment, participants judged whether two visual dot
patterns are the same exemplar (cf. "p" and "p") or not (cf. "p" and "P")
more efficiently when the comparison items were presented directly to the
same hemisphere than to different hemispheres. However, they judged whether
patterns belong to the same category of shape (cf. "p" and "P") or not (cf.
"p" and "S") more efficiently when the items were presented directly to
different hemispheres than to the same hemisphere. Concurrently developed
neural network models with simulated hemispheres were trained to perform
the same tasks as in the human behavioral experiment. Explanations for the
human behavioral results are related to architectural and functional
aspects of the networks.
2
Binding What, Where, and When in Object Identification
Michael D. Anes,
Jacqueline Liederman, and Takeo Watanabe
Vision Science Laboratory,
Boston University,
Department of Psychology,
michanes@bu.edu
Two priming experiments investigated object representations with several
conflicting attributes. Participants identified a single numeral after
seeing moving numerals. Numeral identity (same as/different from moving
numerals) and location (same as/shifted from trajectory endpoint) were
manipulated in both experiments. In Experiment 2, multiple visual features
(numeral frame shape, frame color and font) were also manipulated
simultaneously. Reaction time increased after identity and location
changes, with no interaction of factors in both experiments. Changing
multiple visual features had significant negative effects, unlike single
feature changes in other tasks. Location by feature interactions obtained:
identification was facilitated by a) holding features constant if identity
and location provided "same object" evidence and b) changing features if
identity and location indicated a "new object". Experiment 3 manipulates
temporal parameters in the task. We suggest a) limitations exist in binding
some dorsal and ventral attributes yet b) interactive processing of other
attributes provides redundancy gain in cases of both perceptual stability
and disruption.
3
An attractor field model of face representation: Effects of
typicality and image morphing
Marian Stewart Bartlett, James W. Tanaka
Salk Institute
Marian Stewart Bartlett, Ph.D.
Computational Neurobiology Lab
The Salk Institute
10010 N. Torrey Pines Road
La Jolla, CA 92037
marni@salk.edu,
Phone: (619)453-4100 x1420,
Fax: (619)587-0417
http://www.cnl.salk.edu/~marni
A morphed face image at the midpoint between a typical face and an atypical
face tends to be perceived as more similar to the atypical parent than the
typical parent (Tanaka, Kremen, & Giles, 1997). One account of this
atypicality bias is provided by the hypothesis that face representations
are characterized as fields of attraction in face space. Atypical faces
have larger attractor fields than typical faces since they are farther from
the origin of face space where the density of faces is much lower. We test
this hypothesis on a set of graylevel face images. We first demonstrate
that feedforward models based on principal component analysis, which have
accounted for other face perception phenomena, cannot account for the
atypicality bias. Next we show that the density of face space is greater
near typical faces than atypical faces, and typical faces are closer to the
origin of face space than atypical faces. Finally, an attractor network
model of face representations is implemented, and the attractor fields are
examined by presenting morphed faces to the network.
4
Dissociable Mechanisms for Priming of Planar-Rotated Unfamiliar
Objects
E. Darcy Burgund & Chad J. Marsolek
Department of Psychology, University of Minnesota,
75 East River Road, Minneapolis, MN 55455,
dburgund@levels.psych.umn.edu, Tel. (612) 626-0807,
(612) 626-1546 Fax:(612) 626-2079
Typically, recognition is impaired when objects are disoriented in
the plane. We investigated whether dissociable neural subsystems
underlie recognition of disoriented objects in qualitatively different
ways. Participants decided whether laterally presented unfamiliar
objects were structurally possible or impossible, after encoding
objects in the central visual field. Test objects were presented in the
same or different orientation (by 90 or 180 degrees) compared with
encoding, and orientation-specific priming was measured as a
greater bias to respond "possible" to same- than to different-
orientation objects. When objects were presented directly to the
right hemisphere, orientation-specific priming (in the relatively fast
responses) was observed when objects were re-oriented by 90
degrees, but not by 180 degrees. When objects were presented
directly to the left hemisphere, orientation-specific priming (in the
relatively slow responses) was observed when objects were re-
oriented by 90 or 180 degrees. We relate these findings to current
theories of object representation.
5
How well do chess masters remember famous chess positions?
Implications for theories of expertise
Christopher F. Chabris, Daniel J. Benjamin, and Daniel J.
Simons
Department of Psychology,
Harvard University,
33 Kirkland Street,
Cambridge, MA 02138 USA,
cfc@wjh.harvard.edu,
Tel. 1-617-876-5759,
Fax 1-617-491-9570
Abstract ( < 150 words): Two experiments tested whether the memory
representations used by chess masters (1) are lists of familiar clusters
or chunks of chess pieces or (2) include only information about important
or relevant pieces. First, 23 masters recognized famous chess positions
they were likely to have previously studied. When a position was modified
from the correct one, subjects detected the change more often if it
affected the "meaning" of the position than if it did not, even if the
non-meaningful change affected more pieces. Second, one grandmaster
recalled a similar set of positions without prior study; most of his
errors did not alter the meaning of the positions. In each case memory for
unimportant pieces was retained as well, though not as strongly as for
important pieces. These results support a hybrid model in which chunks of
pieces, global categories, and meaning are all represented in the visual
memory of chess masters.
6
Influences of spatial context on novel object recognition
C.G. Christou, B.S. Tjan and H.H. Bülthoff
Address: Max-Planck-Institute for Biological Cybernetics, Spemannstrasse 38
Tuebingen 72076, Germany, chris@kyb.tuebingen.mpg.de,
Telephone: 49 7071 601630,
Fax: 49 7071 601616
The visual recognition of novel objects is influenced by the degree of
deviation from studied viewing direction, especially when their geometric
structure cannot be decomposed into view-invariant components. In a natural
context, changes in the appearance of an object are often caused by changes
in the observer's vantage point. Moreover, these changes are almost always
apparent to the observer and could in principle be used in the recognition
process. We investigated the use of implicit viewer vantage point
information by constructing a highly realistic virtual living room which
was rich in visual depth information and in which subjects could make
simulated movements. On a pedestal in the middle of the room, we placed
various 3D geometrical objects. After an initial exploratory period, in
which subjects familiarised themselves with the room, training and
recognition tests were conducted. In long-term encoding and recognition
tasks we observed an improvement in performance when testing occurred with
the room visible than when testing occurred without the room. To test if
this benefit derives from the room providing implicit vantage-point
information we repeated the object identification task while randomly
perturbing the orientation of the room with respect to the objects. We
found that performance in this case was poorer in comparison to when no
room was present. These results indicate that in the recognition of novel
objects, people can make use of implicit information specifying where they
are and where they are looking.
7
Visuospatial Constructive Ability of People with Williams Syndrome
Alexandra Fonaryova Key, John R. Pani, and Carolyn B. Mervis
Department of Psychology, University of Louisville,
Louisville, KY 40292, a0fona01@ulkyvm.louisville.edu,
Tel. (502) 852-4639, Fax: (502) 852-8904
Williams syndrome is a genetic disorder characterized by mild to moderate
mental retardation or learning disabilities. Because Williams syndrome is
associated with a characteristic pattern of cognitive strengths and
weaknesses, full-scale IQ masks large discrepancies across different types
of abilities. Visuospatial construction is the domain of greatest weakness
for individuals with Williams syndrome. In our presentation, we briefly
summarize three studies of spatial cognition in individuals with Williams
syndrome and describe our working hypotheses regarding the nature of their
difficulty with visuospatial construction. In particular, it appears that
they have difficulty in changing spatial organization.
8
Perceiving Curvilinear Heading in the
Presence of Moving Objects
Nam-Gyoon Kim and Brett R. Fajen
Department of Psychology, Box U-20, 406 Babbidge Road,
University of Connecticut, Storrs, CT 06269-1020,E-mail: brf93003@uconnvm.uconn.edu, Tel.(860) 486-2212,Fax: (860) 486-2760,
Four experiments were directed at understanding the influence of
multiple moving objects on curvilinear (i.e., circular and elliptical)
heading perception. Displays simulated observer movement over a ground
plane in the presence of moving objects, depicted as transparent,
opaque or black cubes. Objects either moved parallel to or intersected
the observerÕs path, and either retreated from or approached the moving
observer. Heading judgments were accurate across all conditions, but
perceptual biases did occur. Whereas transparent objects elicted a bias
in perceived heading direction that depended on the objectsÕ motion,
opaque and black objects tended to elicit a weaker bias. Discussion
focused on the significance of these results for computational models
of heading perception and the possible role of dynamic occlusion
9
Evaluating the Componential Assessment of Visual Perception
test (CAVP) as a measure of visual performance in the learning disabled.
Lemon L, Robertson KM, Jutai J, Steffy R.
School of Optometry, University of Waterloo,
Waterloo, Ontario N2L 3G1,
sarik@golden.net,
Tel: 1-519-742-1579,Fax: 1-519-725-0784
A computerized test, The Componential Assessment of Visual Perception
(CAVP) has been designed to measure areas of visual perception most
pertinent to academic performance. The CAVP measures the ability to
adequately filter out irrelevant information by scoring the response time
(search scores) with different memory loads (memory requirements). Search
scores are taken in high distraction mode or in low distraction mode. The
CAVP was applied to evaluate a learning disabled population who previously
demonstrated anomalies in visual perception on a specific battery of tests.
Subjects were selected from the Waterloo Psycho-Educational Neurometric
Program (WATPEN). Their results on the CAVP were compared to a normal
control group. The total test time required for the WATPEN selected
subjects to complete the CAVP was significantly greater than the total test
time of normal control group. The WATPEN subjects who were identified as
having visual perception difficulties demonstrated a higher search score
(total test time) then the normal population. Potentially, the CAVP could
be used as a clinical and/or educational tool to screen possible visual
perception problems.
10
Part-set cueing effect in visual object recognition.
Qiang Liu & Michael J. Wenger
Department of Psychology,
Social Science II,
University of California,
Santa Cruz, CA 95064,
qxliu@cats.ucsc.edu ,Office: (831) 459-5679, FAX: (831) 459-3579
When participants are asked to remember a set of study items
and at test are given part of the set as cues to recall the remaining items,
provision of these cues often impairs performance on the remaining items
(e.g., Slamecka, 1968, 1969; Watkins, 1975; Muller & Watkins, 1977; Rundus,
1973; Roediger, 1973). It has been suggested that this is a relatively general
phenomenon, but it has not consistently been demonstrated in memory for
visual objects nor across a range of memory tasks. Numerous hypotheses have
been formulated to explain this phenomenon; some suggest a
decisional basis while others contend that it is a memory effect. One
way of assessing this is through the use of signal detection measures in
a recognition task. The present experiment employed an old/new
recognition task using 36-item sets of photographic images (composed of
faces of men and women, cats, dogs, car grills, and geometric figures).
After studying a set of images, participants were given either
0, 6, 12, or 18 of the study items as intra-list cues before the old/new
recognition task. The overall analysis included the hit and false alarm
rates, P(C), d' and c. Analysis of the hit rate demonstrated the part-set
cueing effect was obtained, and the false alarm rate also decreased as a
function of the number of cues provided. However, d', a measure of
memory strength, did not vary across levels of cueing, whereas the measure of
decisional criterion, c, did change significantly as a function of the
number of cues given. Thus, the inhibitory effect of part-set cues in
recognition seems to be a result of changes in decision criterion rather
than changes in memory strength.
11
Perceived Lightness as a Measure of Perceptual Grouping
Michael C. Mangini, Irving Biederman, and Elizabeth K. Williams
Hedco Neuroscience Building, MC 2520,
University of Southern California,
Los Angeles, CA 90089-2520,
mangini@usc.edu, bieder@usc.edu,
Tel. (213) 740-6102, Fax: (213) 740-5687
The standard interpretation of simultaneous contrast, in
which, for example, a gray bar on a black background appears lighter
than when on a white background, has been that of lateral inhibition.
What would happen if the gray bar is flanked with noncontiguous white
bars on the black background (so the set of bars resembles a picket
fence)? Gilchrist and his associations (e.g., Economou, Annan, &
Gilchrist, 1998) have recently demonstrated that, surprisingly, the
effect of the background disappears and the contrast is solely produced
by the effects of the contextual bars, which he termed ³reversed
contrast² (RC). These investigators reported several manipulations
suggesting that the magnitude of the RC effect was a function of the
strength of the perceptual grouping of the gray and context bars. We
report a series of experiments designed to investigate further whether
the variations in perceived brightness reflect the presumed
organization of complex shapes. In the first two experiments we
replicated the RC effect, and show that a contiguous gray bar that is
not grouped with the contextual bars (because it is at right angles and
partially occluded by them) is unaffected by their presence. However, a
possible residual effect of lateral inhibition was also present. A
third experiment investigated the relation between the RC effect and
whether the context was grouped into the same or different parts of the
same figure by varying whether the parts were joined by T or L
vertices. No effect of differences in part grouping strength was
observed.
12
Spatial summation of facial images reveals configural processing
Paolo Martini & Ken Nakayama
Vision Sciences Lab, Dept. of Psychology,
Harvard University,
33 Kirkland St., 7F,
Cambridge MA 02138,
pmartini@wjh.harvard.edu,
Tel.: 617-495-3884,
Fax: 617-495-3764
Humans code faces not as collections of independent features, but in
a more synthetic way that sacrifices features' independence. Such
holistic coding is intolerant to misorientation: inverted faces are
decomposed into parts (see the "Margaret Thatcher illusion"). Using
the technique of spatial summation we explore this effect and show
that faces degraded by noise are perceived as wholes only when
upright. By segmenting faces in blocks we measured S/N thresholds
for discrimination of face pairs in a 2AFC paradigm as a function of
percentage of face area shown. Spatial integration was poor for
inverted and scrambled faces, suggesting decomposition into
individual features. Upright faces showed a similar trend over small
areas, but with larger areas discrimination became more resistant to
noise, suggesting holistic processing. Moreover, discrimination
thresholds for complete upright faces, but not for inverted or
scrambled, approached detection levels.
13
Categorical perception of face identity in noise: A method for
isolating configural processing
Elinor McKone Paolo Martini, & Ken Nakayama
Vision Sciences Lab,
Dept. of Psychology,
Harvard University,
33 Kirkland St., 7F,
Cambridge MA 02138,
E-mail: emckone@wjh.harvard.edu,
Telephone: 617-495-3884,
Fax: 617-495-3764
Identification of an upright face could, in principle, occur via local
features
(nose shape, hairstyle), configural information about spatial relationships
between features, or some combination of both. Inversion is believed to
destroy configural processing but, because feature-based identification
remains possible, isolation of configural processing requires identifying a
phenomenon which disappears completely with inversion. We show that
categorical perception (CP) of faces in noise is such a phenomenon. We
added noise to morphs between pairs of initially novel target faces,
obscuring local information. CP was found for upright faces: pairs of
morphs which crossed the category boundary predicted from a binary (Face
1 or Face 2) classification task showed smaller discrimination thresholds
and were rated as more dissimilar. Despite up to 10,000 trials of practice,
however, no CP emerged for inverted faces on either task. Further data
directly demonstrated the role of noise in eliminating feature-based CP.
14
Playing a game can tell a lot about face recognition
Alexa I. Ruppertsberg, Hendrik-Jan van Veen, Galia Givaty, and Heinrich H. Bu¨lthoff
Max-Planck-Institut fu¨r biologische Kybernetik, Spemannstr. 38, 72076 Tu¨bingen, Germany,email: alexa/veen@kyb.tuebingen.mpg.de
We implemented an internet version of the well-known memory game on our
webserver to study viewpoint influences on face recognition. We were
able to attract more than 200 anonymous participants through the
website. Players had to find eight face pairs in a 4-by-4 card array.
There were three different levels at which the game could be played.
Level 1: A pair consisted of two identical frontal faces illuminated
from the front. Level 2: A pair consisted of two symmetric views of a
face: 45 and -45 deg. The 45 deg view was illuminated from the front,
the -45 deg view was illuminated from -45 deg. Level 3: A pair
consisted of two different views: frontal and 45 deg, both illuminated
from the front. Players could only reach the next level by finishing
the previous one. Quitting the game was allowed at any time. We
analyzed the number of errors participants made until finishing each
level.
Result: Players made more errors on level 3 than on level 2, and more
on level 2 than on level 1. To test for possible learning effects (the
faces were kept the same in all levels) another group of players played
the levels in a different order. However, error rates were independent
of the order in which the levels were played. Apparently, using
bilateral symmetry inherent in the face seems to be easier (in the
sense of less errors made), than to make use of a common illumination
direction. This is consistent with a study by Troje and Bu¨lthoff
(Vision Research 38,1,1998) where a same/different paradigm in a
precisely timed lab experiment using untextured faces was employed. The
results of our game paradigm show that their results can be extended to
other paradigms, longer presentation times, and textured faces. When
lab members (n=16) who were familiar with the faces (their colleagues)
played the game, their error over all levels did not vary, suggesting a
rather image-independent but semantic-dependent behavior. Conclusion:
The usage of a game paradigm challenges and motivates participants and
allows to draw conclusions about mechanisms in face recognition.
14
Change Blindness and Exogenous Attentional Capture
Brian J. Scholl
Rutgers Center for Cognitive Science,
Rutgers University, Busch Campus,
Psychology Bldg, New Annex,
New Brunswick, NJ 08903,
scholl@ruccs.rutgers.edu,
http://ruccs.rutgers.edu/~scholl,
Tel : 732-445-6163, FAX : 732-445-6715
When two scenes are alternately displayed, separated by a mask, even
large, repeated changes between the scenes often go unnoticed for
surprisingly long durations. Change blindness of this sort is
attenuated at "centers of interest" in the scenes, however, supporting
a theory of scene perception in which attention is necessary to
perceive such changes in scenes (Rensink, O'Regan, & Clark, 1997).
Problems with this measure of attentional selection -- via verbally
described 'centers of interest' -- are discussed, including worries
about describability and explanatory impotence. Other forms of
attentional selection, not subject to these problems, are employed in
two 'flicker' experiments. Attenuated change blindness is observed at
attended items when attentional selection is realized via involuntary
exogenous capture of visual attention (to late-onset items and color
singletons), even when these manipulations are uncorrelated with the
loci of the changes, and are thus completely irrelevant to the change
detection task. These demonstrations ground the attention-based theory
of change blindness in a type of attentional selection which is
understood more rigorously than are 'centers of interest'.
15
Memory for spatial layout from visual and tactile experience
Amy L. Shelton and Timothy P. McNamara
Department of Psychology, 301 Wilson Hall, Vanderbilt Univ.,
Nashville, TN 37240, amy.l.shelton@vanderbilt.edu,
Telephone: (615)322-6050, (615)662-4984,
Fax: (615) 343-8449
Previous research on orientation dependence in
spatial memory has relied primarily on visual experience; however, much of
our daily experiences also involve the actions we perform within space.
This study examined both visual and tactile/motor experience in spatial
learning and memory. Participants viewed a display of objects from one
perspective and reconstructed the display from either the same perspective
or a novel perspective using only tactile information. Performance on
judgments of relative direction and scene recognition revealed best
performance on the orientation corresponding to the reconstructed
perspective. These results indicate that the addition of a generative
motor task did not yield an orientation independent representation.
Moreover, people preferred the view generated during tactile reconstruction
over the view experienced visually, suggesting that generating a
perspective produced a stronger representation in memory than direct
viewing.
16
Does human object recognition use independent shape dimensions?
Brian J. Stankiewicz
University of Minnesota
Three experiments investigate whether human object recognition represents
three- dimensional object shape using independent shape dimensions. The
answer to this question is crucial if one hopes to resolve how the brain
represents three-dimensional object shape. Experiment 1 used an object
recognition task in which subjects discriminated between two metrically
different volumes that differed in their aspect-ratio or primary-axis
curvature. Shape noise was parametrically added to these two dimensions.
Results from experiment 1 are consistent with the independent processing of
an object's aspect ratio and curvature. Experiment 2 asked whether the
visual system can represent any orthogonal shape dimensions independently.
Experiment 2 used two orthogonal that were linear combination of aspect
ratio and primary-axis curvature. Results from Experiment 2 suggest that
subjects do not readily treat all orthogonal shape dimensions
independently. Experiment 3 investigated how these shape dimensions are
combined in a cue-combination experiment. Results from this experiment are
consistent with the independent processing of primary-axis curvature and
aspect ratio.
17
The Roles of the Magnocellular and Parvocellular Systems in the Perception
of Dynamic Forms
Yukari Takarae, Lawrence E. Melamed
Kent State University,
Michael K. McBeath
Arizona State University
Psychology Department, Kent State University,
Kent, OH 44242, ytakarae@kent.edu,
Telephone: (330)672-2166
Although many studies have demonstrated that there are two distinct
functional streams in the human visual system, recent evidence suggests
that these systems interact with each other extensively. The current study
was designed to investigate the roles of the magnocellular and
parvocellular systems in dynamic form perception. A form discrimination
task was used whose target was indicated by dynamic occlusion. Hues and
contrast of display elements were manipulated according to the existing
models of parallel pathways in the visual system in order to alter
activation levels of the magnocellular and parvocellular pathways.
Participants' response accuracy was strongly influenced by target speed and
background hue. The results suggest that the perception of target shapes
was mediated by two separate systems depending on the target speed, and the
likely candidates for these systems are the magnocellular and parvocellular
systems.
19
Pointing to hidden landmarks is similar in real and virtual environments
H.A.H.C. van Veen, K. Sellen, and H.H. Buelthoff
Max-Planck-Institute for Biological Cybernetics,
Spemannstrasse 38, 72076 Tuebingen, Germany,
hendrik-jan.veen@tuebingen.mpg.de,
phone +49 7071 601631 ; fax +49 7071 601616
More and more researchers are acknowledging the significance of virtual
environments for the study of human perception and behaviour. Especially
when studying abilities for which the human-in-the-loop element forms a
key ingredient -- such as in wayfinding and visually guided locomotion
-- do virtual reality techniques constitute an increasingly popular tool
for research.
We try to develop a better understanding of the advantages and
disadvantages of this approach by comparing perception and spatial
behaviour in real and virtual environments. The current study compares
pointing accuracy in an outdoor environment (a 600 by 400 m section of
the highly irregular centre of Tuebingen) with that in a corresponding
virtual environment. Standing near one of eleven well-known landmarks,
subjects (n=10) had to turn a pointer in the estimated direction of each
of the other ten invisible (occluded) landmarks. This procedure was
repeated from all eleven locations along the subjects' route through
town (all subjects knew the city very well). The second experiment was
conducted in the laboratory with the same group of subjects. They were
seated in the middle of a 7m diameter half-circular projection screen on
which 180 by 48 degree fragments of panoramic photographs taken near
each of the above mentioned landmarks were displayed. Pointing was
accomplished by rotating the image until the object of interest was
thought to be in the straight ahead direction.
The results show that errors made in the virtual environment are quite
similar to errors made outdoors: the mean absolute pointing error was
only slightly better outdoors (10.9±0.4deg) than in the laboratory
(12.9±0.5deg). The pattern of systematic errors was strikingly similar
between the two environments.
We conclude that a) subjects are capable of using spatial knowledge
acquired in a real environment for accurately orienting themselves in
the corresponding virtual environment, and b) the role of artificial
pictorial cues introduced by the (large) projection screen is negligible
for pointing tasks.
20
When Does Variation in Contrast Polarity Affect Contour Grouping in Object Recognition?
Edward A. Vessel,Suresh Subramaniam, & Irving Biederman
Hedco Neuroscience Building, MC 2520,
University of Southern California,
Los Angeles, CA 90089-2520,
E-mail: vessel@usc.edu,
Tel: (213) 740-6102, (213) 740-6094
Fax: (213) 740-5687
When the sections of a contour can be grouped according to
smooth collinearity or curvilinearity, there is no effect of variations
in contrast polarity, so that an all-black or all-white object on a
gray background is named as rapidly as an object where half of each
contour is white and the other half black (as in Fig. 2 below,
Subramaniam, 1998; see also Economou, Annan, & Gilchrist, et al.,
1998; Spehar, 1998). We assessed the effects of variations in contrast
polarity at contour endings in a series of object naming experiments in
which sections of the objects' contours were deleted in midsegment to
produce gaps . Small additional contours were added at right angles to
both line endings at each gap to produce a pair of L-vertices in one
condition and T-vertices in another. When the additional contours were
of the same polarity as the object's contours, e.g., so the legs of the
L were both black on a gray background, naming performance was much
worse than that for objects with all-black T vertices, consistent with
Hummel and Biederman's (1992) claim that grouping is suppressed (or not
supported) through L vertices. However, when the additional contours
differed in polarity from that of the object (so, for example, one of
the legs of the L-vertex was white and the other black), grouping of
the legs of the L was suppressed and the grouping of the object's
contours was facilitated so that naming performance was equivalent for
objects whose gaps were bridged by L and T vertices. These results are
derivable from a theory that would build detectors based on the
statistics of images in that changes of contrast polarity are common
along a length of contour but extremely rare at the point of a vertex.
The results imply that end-stopped cells supporting object
recognition--unlike complex cells--should be sensitive to the direction
of contrast.
21
Representation of Object relationship and Environment Shape
Frances Wang & Elizabeth S. Spelke
Massachusetts Institute of Technology
Do humans and other animals use an allocentric reference frame and
represent spatial positions independently of their own heading and
position, or do they use an egocentric reference frame and form spatial
representations that alter as they move? Our experiment studied the
effects of disorientation on accuracy of spatial relationships among
objects and among features of the environment shape. Subjects pointed to
objects or corners of a chamber with eyes-covered, before and after
disorientation by spinning in a chair. Internal consistency among object
positions is significantly reduced after disorientation, meaning
representations of object relationships rely on one's sense of orientation,
thus supports the egocentric representation hypothesis. On the contrary,
relative errors among the corners are the same before and after
disorientation, supporting an allocentric representation hypothesis.
Ongoing studies are investigating whether this distinction reflects single
or multiple systems, and whether it is due to the symmetry of the chamber.
22
Geometrical constraints on the perception of 3-D objects
Willems, B. & Wagemans, J. (Department of Psychology, University of Leuven, Belgium)
Bert Willems
University of Leuven
Department of Psychology
Tiensestraat 102
B-3000 Leuven
Belgium
Bert.Willems@psy.kuleuven.ac.be
We investigated the conditions under which subjects
are able to discriminate between an orthogonal and an oblique cross (i.e.,
with a 75 deg angle). The projection of this 3-D angle depends on the
viewpoint from which the cross is seen which we manipulated experimentally by
varying the position of the cross in depth. We found that accuracy
deteriorated with increasing foreshortening of the two legs defining the 3-D
angle. For each position of the cross we calculated the
uncertainty-distribution over the 2-D angle, given an uncertainty over the
3-D location of the cross. We found that the variance of these
uncertainty-distributions was much higher with increasing foreshortening of
the two legs. This type of research should help to clarify some of the
confusion surrounding viewpoint-dependency of 3-D object recognition (e.g.,
the distinction between 'good' or canonical and 'bad' or foreshortened views
of 3-D objects).
23
Recognizing Rotated Faces: Properties of Symmetric Relations
Safa R. Zaki & Thomas A. Busey
Psych Dept., Indiana Univ.
Bloomington IN 47405,
szaki@indiana.edu,
(812) 855-4261,
(812) 855-4691 (fax)
Models derived from categorization work are applied to the recognition of
rotated faces. We find evidence for the use of symmetric relations when
recognizing faces at angles that are near-mirror images of studied views.
However, the use of these symmetric relations appears only under specific
conditions in which subjects are asked to recognize old faces at any
orientation. Multidimensional scaling fits derived from similarity ratings
are used as input to a number of quantitative models that describe the
recognition processes within a geometric framework.
24
Light from shadow: Is it a perceptual object?
Daniele Zavagno & Manfredo Massironi
Dr. Daniele Zavagno, Dipartimento di Psicologia Generale,
Universita' di Padova, Via Venezia 8, 35131 Padova, Italy,
E-mail: dzavagno@psico.unipd.it,
Telephone: office: ++39-49-8276671 / Lab: ++39-49-8276922,
Fax: ++39-49-8276600
Author List: Daniele Zavagno* & Manfredo Massironi**;
*Dipartmento di Psicologia Generale, Universitý di Padova;
**Istituto di Psicologia, Universitý di Verona
It is studied the possibility to see light as the
illuminating agent in achromatic visual scenes. In some cases light can
have a very strong phenomenal evidence, and we called such evidence
surface light. Our hypothesis is that the perceptual experience of surface
light is linked to the organization of cast shadows inside the visual
scene. We tested the hypothesis on a group of 19 subjects using
Renaissance achromatic engravings as stimuli. Two factors seem to be
important for the appearance of surface light: i) high contrast among
illuminated areas and shadows; ii) presence of cast shadows inside the
scene. The last factor invokes the role played by margins in visual
perception: the collection of cast shadows inside the visual scene
determines a new set of margins that overlaps the set of margins that
regulate figure-ground organization. When this overlap is transversal and
there is a high luminance contrast ratio between light areas and dark
areas, surface light is perceived.
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and was last updated on 8/23/98