Showing papers by "Frans A. J. Verstraten published in 2011"
TL;DR: Three areas in object selective cortex, the lateral occipital cortex area (LO), the fusiform face area (FFA), and the parahippocampal place area (PPA), robustly code the spatial position of objects, which suggests a potential neural solution to accomplishing translation invariance.
63 citations
TL;DR: Grouping was additionally affected by orientation: identical orientations were grouped longer than dissimilar orientations, even when presented to different eyes, and grouping effects were further modulated by the distribution of the targets across the visual field.
Abstract: During binocular rivalry, perception alternates between dissimilar images presented dichoptically. Although perception during rivalry is believed to originate from competition at a local level, different rivalry zones are not independent: rival targets that are spaced apart but have similar features tend to be dominant at the same time. We investigated grouping of spatially separated rival targets presented to the same or to different eyes and presented in the same or in different hemifields. We found eye-of-origin to be the strongest cue for grouping during binocular rivalry. Grouping was additionally affected by orientation: identical orientations were grouped longer than dissimilar orientations, even when presented to different eyes. Our results suggest that eye-based and orientation-based grouping is independent and additive in nature. Grouping effects were further modulated by the distribution of the targets across the visual field. That is, grouping within the same hemifield can be stronger or weaker than between hemifields, depending on the eye-of-origin of the grouped targets. We also quantified the contribution of the previous cues to grouping of two images during binocular rivalry. These quantifications can be successfully used to predict the dominance durations of different studies. Incorporating the relative contribution of different cues to grouping, and the dependency on hemifield, into future models of binocular rivalry will prove useful in our understanding of the functional and anatomical basis of the phenomenon of binocular rivalry.
29 citations
TL;DR: This work found discrimination performance to be increased if features were perceptually bound into an object and detection performance was higher within and lower outside the bound object as compared to the unbound configuration.
Abstract: Object-based attention facilitates the processing of features that form the object. Two hypotheses are conceivable for how object-based attention is deployed to an object's features: first, the object is attended by selecting its features; alternatively, a configuration of features as such is attended by selecting the object representation they form. Only for the latter alternative, the perception of a feature configuration as entity ("objecthood") is a necessary condition for object-based attention. Disentangling the two alternatives requires the comparison of identical feature configurations that induce the perception of an object in one condition ("bound") and do not do so in another condition ("unbound"). We used an ambiguous stimulus, whose percept spontaneously switches between bound and unbound, while the stimulus itself remains unchanged. We tested discrimination on the boundary of the diamond as well as detection of probes inside and outside the diamond. We found discrimination performance to be increased if features were perceptually bound into an object. Furthermore, detection performance was higher within and lower outside the bound object as compared to the unbound configuration. Consequently, the facilitation of processing by object-based attention requires objecthood, that is, a unified internal representation of an "object"-not a mere collection of features.
18 citations
16 citations
TL;DR: The results suggest that an element that attracts eye movements following short saccade latencies does so because it is the only element processed at that time, and the temporal constraints of processing visual information seem to be a determining factor in saccadic selection.
Abstract: It has been suggested that independent bottom-up and top-down processes govern saccadic selection. However, recent findings are hard to explain in such terms. We hypothesized that differences in visual-processing time can explain these findings, and we tested this using search displays containing two deviating elements, one requiring a short processing time and one requiring a long processing time. Following short saccade latencies, the deviation requiring less processing time was selected most frequently. This bias disappeared following long saccade latencies. Our results suggest that an element that attracts eye movements following short saccade latencies does so because it is the only element processed at that time. The temporal constraints of processing visual information therefore seem to be a determining factor in saccadic selection. Thus, relative saliency is a time-dependent phenomenon.
15 citations
TL;DR: Perception during the dominance phase of rivalry is affected by a suppressed image as if it were visible, and the pattern of interference by the suppressed image is qualitatively similar to the situation where this image and the probe are simultaneously visible.
Abstract: During binocular rivalry, perception alternates between dissimilar images that are presented dichoptically. It has been argued that perception during the dominance phase of rivalry is unaffected by the suppressed image. Recent evidence suggests, however, that the suppressed image does affect perception of the dominant image, yet the extent and nature of this interaction remain elusive. We hypothesize that this interaction depends on the difference in feature content between the rivaling images. Here, we investigate how sensitivity to probes presented in the image that is currently dominant in perception is affected by the suppressed image. Observers performed a 2AFC discrimination task on oriented probes (Experiment 1) or probes with different motion directions (Experiment 2). Our results show that performance on both orientation and motion direction discrimination was affected by the content of the suppressed image. The strength of interference depended specifically on the difference in feature content (e.g., the difference in orientation) between the probe and the suppressed image. Moreover, the pattern of interference by the suppressed image is qualitatively similar to the situation where this image and the probe are simultaneously visible. We conclude that perception during the dominance phase of rivalry is affected by a suppressed image as if it were visible.
13 citations
TL;DR: In this paper, the authors used functional magnetic resonance imaging (FMRI) and multivariate pattern classification to directly compare the neural activity evoked during the observation of both real and illusory motions.
Abstract: In the motion aftereffect (MAE), adapting to a moving stimulus causes a subsequently presented stationary stimulus to appear to move in the opposite direction Recently, the neural basis of the motion aftereffect has received considerable interest, and a number of brain areas have been implicated in the generation of the illusory motion Here, we use functional magnetic resonance imaging in combination with multivariate pattern classification to directly compare the neural activity evoked during the observation of both real and illusory motions We show that the perceived illusory motion is not encoded in the same way as real motion in the same direction Instead, suppression of the adapted direction of motion results in a shift of the population response of motion sensitive neurons in area MT +, resulting in activation patterns that are in fact more similar to real motion in orthogonal, rather than opposite directions Although robust motion selectivity was observed in visual areas V1, V2, V3, and V4, this MAE-specific modulation of the population response was only observed in area MT + Implications for our understanding of the motion aftereffect, and models of motion perception in general, are discussed
12 citations
TL;DR: It is shown that within-task trial-by-trial behavioral variability in attentional selection latency correlates to trial- by-trial variability in ERP latency, which was true in a posterior contralateral region, and in central and frontal areas, thereby implicating these as waypoints along which visual information flows on the way to visual awareness.
Abstract: The "neural correlate" of perceptual awareness is much sought-after. Here, we present an novel approach to the identification of possible neural correlates, in which we exploit the temporal connection that inevitably links the selection process that determines what we become aware of, and the development of awareness itself. Because the speed of selection determines when downstream processes can first become involved in generating awareness, the latency of neural processes provides a way to isolate the neural correlates of awareness. We recorded event-related potentials (ERPs) while observers carried out a visual behavioral task designed to estimate attentional selection latency. We show that within-task trial-by-trial behavioral variability in attentional selection latency correlates to trial-by-trial variability in ERP latency. This was true in a posterior contralateral region, and in central and frontal areas, thereby implicating these as waypoints along which visual information flows on the way to visual awareness.
8 citations
TL;DR: It is found that eye movements are biased toward areas with little crowding for conditions where a target could be discriminated peripherally, and this bias reversed to areas with strong crowding, suggesting a dual role for crowding in visual search.
Abstract: We investigated the role of crowding in saccadic selection during visual search. To guide eye movements, often information from the visual periphery is used. Crowding is known to deteriorate the quality of peripheral information. In four search experiments, we studied the role of crowding, by accompanying individual search elements by flankers. Varying the difference between target and flankers allowed us to manipulate crowding strength throughout the stimulus. We found that eye movements are biased toward areas with little crowding for conditions where a target could be discriminated peripherally. Interestingly, for conditions in which the target could not be discriminated peripherally, this bias reversed to areas with strong crowding. This led to shorter search times for a target presented in areas with stronger crowding, compared to a target presented in areas with less crowding. These findings suggest a dual role for crowding in visual search. The presence of flankers similar to the target deteriorates the quality of the peripheral target signal but can also attract eye movements, as more potential targets are present over the area.
8 citations