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Member-Initiated Symposia2012 Symposia Distinguishing perceptual shifts from response biases Human visual cortex: from receptive fields to maps to clusters to perception Neuromodulation of Visual Perception Part-whole relationships in visual cortex Pulvinar and Vision: New insights into circuitry and function What does fMRI tell us about brain homologies?
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Part-whole relationships in visual cortexFriday, May 11, 1:00 - 3:00 pm Organizer: Johan Wagemans, Laboratory of Experimental Psychology, University of Leuven
Symposium DescriptionWith his famous paper on phi motion, Wertheimer (1912) launched
Gestalt psychology, arguing that the whole is different from the sum of the
parts. In fact, wholes were considered primary in perceptual experience, even
determining what the parts are. Gestalt claims about global precedence and
configural superiority are difficult to reconcile with what we now know about
the visual brain, with a hierarchy from lower areas processing smaller parts of
the visual field and higher areas responding to combinations of these parts in
ways that are gradually more invariant to low-level changes to the input and
corresponding more closely to perceptual experience. What exactly are the
relationships between parts and wholes then? Are wholes constructed from
combinations of the parts? If so, to what extent are the combinations additive,
what does superadditivity really mean, and how does it arise along the visual
hierarchy? How much of the combination process occurs in incremental
feedforward iterations or horizontal connections and at what stage does
feedback from higher areas kick in? What happens to the representation of the
lower-level parts when the higher-level wholes are perceived? Do they become
enhanced or suppressed (“explained away”)? Or, are wholes occurring before the
parts, as argued by Gestalt psychologists? But what does this global precedence
really mean in terms of what happens where in the brain? Does the primacy of
the whole only account for consciously perceived figures or objects, and are
the more elementary parts still combined somehow during an unconscious
step-wise processing stage? A century later, tools are available that were not
at the Gestaltists’ disposal to address these questions. In this symposium, we
will take stock and try to provide answers from a diversity of approaches,
including single-cell recordings from V4, posterior and anterior IT cortex in
awake monkeys (Ed Connor, Johns Hopkins University), human fMRI (Scott Murray,
University of Washington), human psychophysics (James Pomerantz, Rice
University), and computational modeling (Jacob Feldman, Rutgers University).
Johan Wagemans (University of Leuven) will introduce the theme of the symposium
with a brief historical overview of the Gestalt tradition and a clarification
of the conceptual issues involved. Shaul Hochstein (Hebrew University) will end
with a synthesis of the current literature, in the framework of Reverse
Hierarchy Theory. The scientific merit of addressing such a central issue,
which has been around for over a century, from a diversity of modern
perspectives and in light of the latest findings should be obvious. The
celebration of the centennial anniversary of Gestalt psychology also provides
an excellent opportunity to doing so. We believe our line-up of speakers,
addressing a set of closely related questions, from a wide range of
methodological and theoretical perspectives, promises to be attracting a large
crowd, including students and faculty working in psychophysics, neurosciences
and modeling. In comparison with other proposals taking this centennial
anniversary as a window of opportunity, ours is probably more focused and
allows for a more coherent treatment of a central Gestalt issue, which has been
bothering vision science for a long time. Presentations Part-whole relationships in vision science: A brief historical review and
conceptual analysis
Johan Wagemans, Laboratory of Experimental Psychology,
University of Leuven Exactly 100 years ago, Wertheimer’s paper on phi motion (1912)
effectively launched the Berlin school of Gestalt psychology. Arguing against
elementalism and associationism, they maintained that experienced objects and
relationships are fundamentally different from collections of sensations. Going
beyond von Ehrenfels’s notion of Gestalt qualities, which involved one-sided
dependence on sense data, true Gestalts are dynamic structures in experience
that determine what will be wholes and parts. From the beginning, this
two-sided dependence between parts and wholes was believed to have a neural
basis. They spoke of continuous “whole-processes” in the brain, and argued that
research needed to try to understand these from top (whole) to bottom (parts )
rather than the other way around. However, Gestalt claims about global
precedence and configural superiority are difficult to reconcile with what we
now know about the visual brain, with a hierarchy from lower areas processing
smaller parts of the visual field and higher areas responding to combinations
of these parts in ways that are gradually more invariant to low-level changes
to the input and corresponding more closely to perceptual experience. What
exactly are the relationships between parts and wholes then? In this talk, I
will briefly review the Gestalt position and analyse the different notions of
part and whole, and different views on part-whole relationships maintained in a
century of vision science since the start of Gestalt psychology. This will
provide some necessary background for the remaining talks in this symposium,
which will all present contemporary views based on new findings. Ventral pathway visual cortex: Representation by parts in a whole object
reference frame
Charles E. Connor, Department of Neuroscience and Zanvyl
Krieger Mind/Brain Institute, Johns Hopkins University, Anitha Pasupathy, Scott
L. Brincat, Yukako Yamane, Chia-Chun Hung Object perception by humans and other primates depends on the ventral
pathway of visual cortex, which processes information about object structure,
color, texture, and identity. Object information processing can be
studied at the algorithmic, neural coding level using electrode recording in
macaque monkeys. We have studied information processing in three
successive stages of the monkey ventral pathway: area V4, PIT (posterior
inferotemporal cortex), and AIT (anterior inferotemporal cortex). At all
three stages, object structure is encoded in terms of parts, including boundary
fragments (2D contours, 3D surfaces) and medial axis components (skeletal shape
fragments). Area V4 neurons integrate information about multiple
orientations to produce signals for local contour fragments. PIT neurons
integrate multiple V4 inputs to produce representations of multi-fragment
configurations. Even neurons in AIT, the final stage of the monkey
ventral pathway, represent configurations of parts (as opposed to holistic
object structure). However, at each processing stage, neural responses
are critically dependent on the position of parts within the whole object.
Thus, a given neuron may respond strongly to a specific contour fragment
positioned near the right side of an object but not at all when it is
positioned near the left. This kind of object-centered position tuning
would serve an essential role by representing spatial arrangement within a
distributed, parts-based coding scheme. Object-centered position sensitivity is
not imposed by top-down feedback, since it is apparent in the earliest
responses at lower stages, before activity begins at higher stages. Thus,
while the brain encodes objects in terms of their constituent parts, the
relationship of those parts to the whole object is critical at each stage of
ventral pathway processing. Long-range, pattern-dependent contextual effects in early human visual
cortex
Scott O. Murray, Department of Psychology, University of
Washington, Sung Jun Joo, Geoffrey M. Boynton The standard view of neurons in early visual cortex is that they
behave like localized feature detectors. We will discuss recent results that
demonstrate that neurons in early visual areas go beyond localized feature
detection and are sensitive to part-whole relationships in images. We measured
neural responses to a grating stimulus (“target”) embedded in various visual
patterns as defined by the relative orientation of flanking stimuli. We varied
whether or not the target was part of a predictable sequence by changing the
orientation of distant gratings while maintaining the same local stimulus
arrangement. For example, a vertically oriented target grating that is flanked
locally with horizontal flankers (HVH) can be made to be part of a predictable
sequence by adding vertical distant flankers (VHVHV). We found that even when
the local configuration (e.g. HVH) around the target was kept the same there
was a smaller neural response when the target was part of a predictable
sequence (VHVHV). Furthermore, when making an orientation judgment of a “noise”
stimulus that contains no specific orientation information, observers were
biased to “see” the orientation that deviates from the predictable orientation,
consistent with computational models of primate cortical processing that
incorporate efficient coding principles. Our results suggest that early visual
cortex is sensitive to global patterns in images in a way that is markedly
different from the predictions of standard models of cortical visual processing
and indicate an important role in coding part-whole relationships in images. The computational and cortical bases for configural superiority
James R. Pomerantz, Department of Psychology, Rice
University, Anna I. Cragin, Department of Psychology, Rice University;
Kimberley D. Orsten, Department of Psychology, Rice University; Mary C.
Portillo, Department of Social Sciences, University of Houston–Downtown In the configural superiority effect (CSE; Pomerantz et al., 1977;
Pomerantz & Portillo, 2011), people respond more quickly to a whole
configuration than to any one of its component parts, even when the parts added
to create a whole contribute no information by themselves. For example,
people discriminate an arrow from a triangle more quickly than a positive from
a negative diagonal even when those diagonals constitute the only difference
between the arrows and triangles. How can a neural or other computational
system be faster at processing information about combinations of parts – wholes
– than about parts taken singly? We consider the results of
Kubilius et al. (2011) and discuss three possibilities: (1) Direct detection of
wholes through smart mechanisms that compute higher order information without
performing seemingly necessary intermediate computations; (2) the “sealed
channel hypothesis” (Pomerantz, 1978), which holds that part information is
extracted prior to whole information in a feedforward manner but is not
available for responses; and (3) a closely related reverse hierarchy model
holding that conscious experience begins with higher cortical levels processing
wholes, with parts becoming accessible to consciousness only after feedback to
lower levels is complete (Hochstein & Ahissar, 2002). We describe a
number of CSEs and elaborate both on these mechanisms that might explain them
and how they might be confirmed experimentally. Computational integration of local and global formJacob Feldman, Dept. of Psychology, Center for Cognitive
Science, Rutgers University - New Brunswick, Manish Singh, Vicky Froyen A central theme of perceptual theory, from the Gestaltists to the
present, has been the integration of local and global image information. While
neuroscience has traditionally viewed perceptual processes as beginning with
local operators with small receptive fields before proceeding on to more global
operators with larger ones, a substantial body of evidence now suggests that
supposedly later processes can impose decisive influences on supposedly earlier
ones, suggesting a more complicated flow of information. We consider this
problem from a computational point of view. Some local processes in perceptual
organization, like the organization of visual items into a local contour, can
be well understood in terms of simple probabilistic inference models. But for a
variety of reasons nonlocal factors such as global “form” resist such simple
models. In this talk I'll discuss constraints on how form- and
region-generating probabilistic models can be formulated and integrated with
local ones. From a computational point of view, the central challenge is how to
embed the corresponding estimation procedure in a locally-connected
network-like architecture that can be understood as a model of neural
computation. The rise and fall of the Gestalt gistShaul Hochstein, Departments of Neurobiology and
Psychology, Hebrew University, Merav Ahissar
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