Biomedical subjects

Marc Pomplun

Publications and source records attributed to Marc Pomplun.

4 recordsLinked to original sources

PubMed2006

Motion misperception caused by feedback connections: a neural model simulating the Fröhlich effect.

When asked to indicate the starting position of a fast moving stimulus, observers do not indicate the actual starting position but a later position on the motion trajectory. This perceptual illusion is known as the "Fröhlich effect". We present a neural model aimed at simulating this phenomenon based on feedforward and feedback connections. The basic simulation mechanisms seem to be compatible with the attentional and the motion extrapolation account. A comparison between simulated and empirical results showed that the model is capable of generating the same main effects as those found in the empirical data.

Feedback↗

PubMed2006

Saccadic selectivity in complex visual search displays.

Visual search is a fundamental and routine task of everyday life. Studying visual search promises to shed light on the basic attentional mechanisms that facilitate visual processing. To investigate visual attention during search processes, numerous studies measured the selectivity of observers' saccadic eye movements for local display features. These experiments almost entirely relied on simple, artificial displays with discrete search items and features. The present study employed complex search displays and targets to examine task-driven (top-down) visual guidance by low-level features under more natural conditions. Significant guidance by local intensity, contrast, spatial frequency, and orientation was found, and its properties such as magnitude and resolution were analyzed across dimensions. Moreover, feature-ratio effects were detected, which correspond to distractor-ratio effects in simple search displays. These results point out the limitations of current purely stimulus-driven (bottom-up) models of attention during scene perception.

Adult↗

PubMed2005

Selectivity for speed gradients in human area MT/V5.

Cortical area MT/V5 in the human occipito-temporal cortex is activated by visual motion. In this study, we use functional imaging to demonstrate that a subregion of MT/V5 is more strongly activated by unidirectional motion with speed gradients than by other motion patterns. Our results suggest that like the monkey homolog middle temporal area (MT), human MT/V5 contains neurons selective for the processing of speed gradients. Such neurons may constitute an intermediate stage of processing between neurons selective for the average speed of unidirectional motion and neurons selective for different combinations of speed gradient and different motion directions such as expanding optical flow patterns.

Adult↗

PubMed2003

Guidance of eye movements during conjunctive visual search: the distractor-ratio effect.

The distractor-ratio effect refers to the finding that search performance in a conjunctive visual search task depends on the relative frequency of two types or subsets of distractors when the total number of items in a display is fixed. Previously, Shen, Reingold, and Pomplun (2000) examined participants' patterns of eye movements in a distractor-ratio paradigm and demonstrated that on any given trial saccadic endpoints were biased towards the smaller subset of distractors and participants flexibly switched between different subsets across trials. The current study explored the boundary conditions of this tendency to flexibly search through a smaller subset of distractors by examining the influence of several manipulations known to modulate search efficiency, including stimulus discriminability (Experiment 1), within-dimension versus cross-dimension conjunction search and distractor heterogeneity (Experiment 2). The results indicated that the flexibility of visual guidance and saccadic bias exemplified by the distractor-ratio effect is a robust phenomenon that mediates search efficiency by adapting to changes in the relative informativeness of stimulus dimensions and features.

Cues↗