Gestalts in the brain - ECVP 2011
- Category: Events
Gestalts in the brain (Wednesday 31st, Auditorium 9:00-11:00)
Co-chairs: Johan Wagemans (Belgium), Hans Op De Beeck (Belgium)
- Johan Wagemans, Belgium : "Gestalts emerging again 100 years later: A modern view on a radical vision"
As a radical alternative to elementalism and associationism, Gestalt theory maintained that experienced objects are fundamentally different from collections of sensations. Gestalts are dynamic structures in experience that determine what will be wholes and parts, based on continuous “whole-processes” in the brain. Already in 1912, Wertheimer hypothesized a physiological short circuit to explain phi motion. Köhler compared the dynamics of self-organization in the brain to the tendency of physical systems to approach maximum order with minimal energy. He also measured cortical currents to support his electrical field theory but experiments by Lashley and Sperry in the 1950s provided stronger counterevidence. After Hubel and Wiesel’s discovery of simple and complex cells in primary visual cortex, neuroscience assumed a predominantly reductionist, elementalist approach. Gestalt phenomena have now become of central interest again but how to understand them within our current views on how the brain operates? Can we decode Gestalts in the fMRI signals somewhere along the visual system’s hierarchy? Do they emerge in the interplay between bottom-up processing, lateral connections, and feedback processing, as synchronization of EEG activity between brain areas, or as traveling waves across the whole brain? These questions are addressed in the symposium on “Gestalts in the brain”.
- Pieter Roelfsema, Netherlands : "How Gestalt rules constrain the spread of attention in visual cortex"
Visual attention can select spatial locations, features and objects. Theories of object-based attention suggest that attention enhances the representation of all parts of an object, even parts that are not task-relevant. However, the automaticity of the spread of attention to parts of an object that are not task-relevant has been disputed because previous studies did not always rule out the possibility of strategic attention shifts. Here we investigated if attention spreads automatically to task-irrelevant features in three macaque monkeys by monitoring neuronal activity in area V1 with chronically implanted electrode arrays. We trained the monkeys to make eye movements to one of two (relevant) image elements and also presented two task-irrelevant image elements that could be grouped with the relevant elements or not. One of these irrelevant image elements was placed in the receptive field of the V1 neurons to investigate if attentional response modulation spreads from the relevant to the irrelevant elements according to a number of Gestalt-grouping cues. Our first experiment tested the spread of attention from relevant to irrelevant contours that were either collinear or orthogonal (good continuation). The second experiment tested if attention spreads from relevant to irrelevant elements with the same or a different colour (similarity). Our third experiment tested the combined influence of colour-similarity and collinearity and the fourth experiment tested the effect of element motion in the same or in a different direction (common fate). When the task-irrelevant image elements in the receptive field were grouped with one of the relevant contour elements, then the selection of this element for an eye movement response influenced V1 activity. Activity was stronger if eye movement target was grouped with the element in the receptive field. In contrast, the effects of eye movement selection were comparatively weak if the relevant and irrelevant image elements were not related by grouping cues. In addition we found that the effects of grouping cues were additive: the strength of the attentional spread in case of grouping by collinearity and colour similarity was the sum of the spread caused by either grouping cue alone. We conclude that enhanced neuronal activity spreads automatically from attended image elements to elements that are not yet attended but are related to them by Gestalt grouping cues. Our results support the hypothesis that enhanced neuronal activity can highlight all the image elements that belong to a single perceptual object, and that it can thereby act to bind them together in perception.
- Mary Peterson, USA : "The neural instantiation of Gestalt principles as uncovered by lesion studies"
The Gestaltists held that figure-ground perception occurred before stored object representations are accessed. On this view, figure-ground processes first determine where a shaped entity (the figure) lies with respect to a border; the figure then accesses memory representations. The groundside of the border lacks shape, and therefore can't access shape memories. This traditional theory replicates figure-ground phenomenology, yet phenomenology doesn't necessarily illuminate process. Indeed, recent evidence indicates that a figure is more likely to be perceived on that side of a border where the parts of well-known objects are present in their familiar spatial configuration rather than in a novel arrangement. Such results support the view that properties of objects that might be perceived on opposite sides of borders are assessed in a fast pass of processing that reaches high levels, including those representing the spatial configuration of well-known objects; properties on opposite sides of borders compete; the winner is perceived as the shaped figure, the loser is perceived as a shapeless ground. This view is consistent with neurophysiological evidence and is supported by tests of visual agnosics, amnesics, and non-brain-damaged individuals, which also reveal a critical role for feedback, supporting a dynamic view of figure-ground perception.
- Hans Op De Beeck, Belgium : "Brain-decoding fMRI reveals the content of neural representations underlying visual Gestalts"
Functional imaging in humans has been very useful to highlight which brain areas are active when global patterns or Gestalts are perceived. However, psychologists and cognitive scientists are not primarily interested in where certain visual properties are computed, but rather in how these properties are computed and the associated content of the neural representations. For example, to understand why “the whole is different from the sum of its parts”, we need to investigate the properties of the representations of the whole and the parts. Recently, it has been shown that the content of neural representations is accessible by the application of multi-voxel pattern analysis methods to functional imaging data. I will describe how these methods can elucidate the representations of parts and wholes and the relationship among them. This will be illustrated with several case studies, including the configural superiority effect and the representation of scenes composed of multiple objects.
- Cees Van Leeuwen, Japan : "Restless minds, wandering brains: The neurodynamics of visual awareness"
Brain activity is, to a large extent, spontaneous activity. Large-scale electrocortical measurement (scalp EEG or MEG) shows that this activity is characterized by a great degree of variability. Yet, this activity is far from random but reveals a patterned structure in space and time. I will discuss the spatiotemporal nature of these patterns, and address the following two questions: does spontaneous activity share some of its characteristics with patterns of EEG (or MEG) activity that are evoked by stimulation and can we identify a meaningful relationship between stimulus information and the properties of evoked activity patterns? I will present evidence that in evoked activity, there are intervals in which synchronized activity spreads through brain regions. The synchronized activity takes the form of traveling or standing waves. The duration of these intervals corresponds to the amount of information in the visual stimulus pattern: the more information in the pattern, the longer the interval duration. I propose that the intervals reflect the time needed to communicate information computed within a brain region to the rest of the brain, and that this activity reflects our awareness of a visual stimulus pattern.