The visual saliency map is non-retinotopic

Marco Boi, Michael Herzog, Marcus Leonardus Vergeer
Pion, 2011
Article de conférence

Résumé

Most visual search models rely on a retinotopic saliency map. Here, we provide evidence that visual saliency is computed non-retinotopically. Recently, it was shown that attention can operate in a non-retinotopic reference frame by inserting a search display in a Ternus-Pikler display [Boi et al, 2009 Journal of Vision 9(13):5, 1–11]. From one frame to another, the display moved back and forth, producing an apparent motion percept. Here, we present an experiment in which the target (a vertically oriented pair of dots) and three distractors (horizontally oriented pairs of dots) were superimposed on non-informative shapes (small red diamonds and green disks). At each frame, the red diamonds turned to green disks and vice versa, while the dot pairs stayed the same. These changes, which occurred in non-retinotopic coordinates, captured attention. As a result, performance in the search task was deteriorated compared to a control condition in which the shapes did not change. Hence, non-retinotopic task-irrelevant stimulus saliency slowed down the search process, arguing for a non-retinotopic saliency map.

Official source

https://infoscience.epfl.ch/record/174372?ln=fr

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Nonretinotopic Exogenous Attention

Marco Boi, Michael Herzog, Marcus Leonardus Vergeer

Attention is crucial for visual perception because it allows the visual system to effectively use its limited resources by selecting behaviorally and cognitively relevant stimuli from the large amount of information impinging on the eyes. Reflexive, stimulus-driven attention is essential for successful interactions with the environment because it can, for example, speed up responses to life-threatening events. It is commonly believed that exogenous attention operates in the retinotopic coordinates of the early visual system. Here, using a novel experimental paradigm [1], we show that a nonretinotopic cue improves both accuracy and reaction times in a visual search task. Furthermore, the influence of the cue is limited both in space and time, a characteristic typical of exogenous cueing. These and other recent findings show that many more aspects of vision are processed nonretinotopically than previously thought.

Elsevier2011

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Perception is usually non-retinotopic. For example, visual perception is stable even though the retinal image is constantly changing due to eye and body movements. Likewise, a reflector on the wheel of a bicycle is perceived to rotate on a circular orbit, while its “true” motion (in retinotopic or exogenous coordinates) is cycloidal. In the first example, the brain uses efference copies to predict and compensate for eye movements. But how does the brain compensate for motion without efference copies? To investigate non-retinotopic motion perception, we used the Ternus-Pikler display. Two disks are flashed on a computer screen. A dot moves linearly up-down in the left disk and left-right in the right disk (retinotopic percept). If a third disk is added alternatingly to the left and right, the three disks form a group moving back and forth horizontally. The dot in the central disk now appears to move on a circular orbit (non-retinotopic percept), because the brain subtracts the horizontal group motion from the combination of the up-down and left-right motion. Here, we asked whether predictability is necessary to compute non-retinotopic motion. In experiment 1, the three disks moved randomly in any direction, rather than horizontally back and forth. Still, a strong non-retinotopic dot rotation was perceived. In experiment 2, we additionally varied the shape and contrast polarity of the stimuli from frame to frame. Still, a strong non-retinotopic dot rotation was perceived. Hence, the visual system can flexibly solve the non-retinotopic motion correspondence problem, even when the retinotopic reference motion is unpredictable. It seems that, in the case of non-retinotopic motion, the brain computes the reference-frame in real-time and does not need efference copy-like signals based on the predictability of the stimulus.

2015

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