Interaction of cognitive and sensorimotor maps of visual space

Attention, Perception, & Psychophysics, 2012

In three experiments, we tested whether sequentially coding two visual stimuli can create a spatial misperception of a visual moving stimulus. In Experiment 1, we showed that a spatial misperception, the flash-lag effect, is accompanied by a similar temporal misperception of first perceiving the flash and only then a change of the moving stimulus, when in fact the two events were exactly simultaneous. In Experiment 2, we demonstrated that when the spatial misperception of a flash-lag effect is absent, the temporal misperception is also absent. In Experiment 3, we extended these findings and showed that if the stimulus conditions require coding first a flash and subsequently a nearby moving stimulus, a spatial flash-lag effect is found, with the position of the moving stimulus being misperceived as shifted in the direction of its motion, whereas this spatial misperception is reversed so that the moving stimulus is misperceived as shifted in a direction opposite to its motion when the conditions require coding first the moving stimulus and then the flash. Together, the results demonstrate that sequential coding of two stimuli can lead to a spatial misperception whose direction can be predicted from the order of coding the moving object versus the flash. We propose an attentional sequential-coding explanation for the flash-lag effect and discuss its explanatory power with respect to related illusions (e.g., the Fröhlich effect) and other explanations. Keywords Attention. Visual illusions. Prior entry At every moment in time, a multitude of visual stimuli impinge on the human retina, but only a few of these stimuli are selected for purposes such as perception, indepth processing, or action control. Attending to different visual locations, stimuli, features, or dimensions boosts the perception and discrimination of fine visual detail (cf. Bashinski & Bacharach, 1980; von Helmholtz 1894) and speeds up processing of visual stimuli at the focus of attention, as well as subsequent saccades to the attended stimuli (cf. Posner, 1980; Rizzolatti, Riggio, Dascola, & Umiltà, 1987). At the same time, attending can prolong the perceived duration of the attended stimuli (cf. Enns, Brehaut, & Shore, 1999; Mattes & Ulrich, 1998). Apart from these effects, visuospatial attention can also contribute to visual illusions. As everyday observers, we are barely aware of these illusions. We naively presume that the temporal and spatial features that we perceive reflect the physical properties of distal objects. Beginning with the early days of experimental psychology, however, visual illusions have shown that spatial features of distal objects can be misperceived (e.g., Fröhlich, 1929), and related research has suggested that attention could be (partly) responsible for these effects (Müsseler & Aschersleben, 1998). Fröhlich observed that the starting position of an abruptly onsetting moving stimulus was not veridically perceived. Instead, it was perceived at a position shifted H.-W.

Perception & Psychophysics, 2000

Classically, it has been assumed that visual space can be represented by a metric. This means that the distance between points and the angle between lines can be uniquely defined. However, this assumption has never been tested. Also, measurements outdoors, where monocular cues are abundant, conflict with this model. This paper reports on two experiments in which the structure of visual space was investigated, using an exocentric pointing task. In the first experiment, we measured the influence of the separation between pointer and target and of the orientation of the stimuli with respect to the observer. This was done both monocularly and binocularly. It was found that the deviation of the pointer settings depended linearly on the orientation, indicating that visual space is anisotropic. The deviations for configurations that were symmetrical in the median plane were approximately the same, indicating that left/right symmetry was maintained. The results for monocular and binocular conditions were very different, which indicates that stereopsis was an important cue. In both conditions, there were large deviations from the veridical. In the second experiment, the relative distance of the pointer and the target with respect to the observer was varied in both the monocular and the binocular conditions. The relative distance turned out to be the main parameter for the ranges used (1-5 m). Any distance function must have an expanding and a compresslllg part in order to describe the data. In the binocular case, the results were much more consistent than in the monocular case and had a smaller standard deviation. Nevertheless, the systematic mispointings remained large. It can therefore be concluded that stereopsis improves space perception but does not improve veridicality.

Cortex, 2004

A complex link exists between vision and unilateral spatial neglect (USN). Firstly, USN is not a perceptual deficit, secondly, USN is not necessarily accompanied by a visual deficit and finally, USN can be observed in non-visual modalities as well as in mental spatial imagery. This apparent supramodality of USN stands in sharp contrast to the fact that neglect signs are often more severe and more durable in the visual than in other sensory modalities .

Vision Research, 2003

When multiple bars are briefly flashed near the saccadic goal on a visual reference just before a saccade, the total width of the multiple bars appears to be compressed toward the saccadic goal. We show that presaccadic compression of visual space is related to the attribution of the displacement of a visual stimulus to the displacement of another stimulus appearing after the saccade. Subjects observed a bar and a ruler. The bar was displaced during a saccade and the ruler disappeared briefly at the same time, and then the ruler reappeared at the same location after the saccade. The subjects had the impression that the bar appeared to remain stationary and the ruler appeared to be displaced after the saccade. This impression occurs strongly when the amount of the compression of visual space reaches the maximum at the saccade onset. Also, it occurs only at the saccadic goal in the same way as presaccadic compression of visual space. Saccadic suppression of displacement was equivalent at the saccadic goal and in the location opposite to the saccadic goal, indicating that the attribution of the bar displacement to the displacement of the ruler appearing after the saccade is not a consequence of saccadic suppression of displacement. Furthermore, performing a direction discrimination task showed that the bar appears stationary at the saccadic goal during compression of visual space even when the bar was actually displaced. We interpret these results as showing that presaccadic compression of visual space establishes the location of the saccadic goal (the bar) as a reference and then the location of the ruler is remapped relative to the reference location after the saccade, resulting in the illusory displacement of the ruler.

Neuron, 2003

Bochum ization, one first has to find a neural correlate of localization. In our search for this correlate, we focused on the 44780 Bochum Germany dorsal stream of the primate brain, as this is commonly thought to be most relevant to encoding where stimuli are (Mishkin et al., 1983). Specifically, we recorded from the medial temporal area (MT), the medial superior tem-Summary poral area (MST), the ventral intraparietal area (VIP), and the lateral intraparietal area (LIP). Not only are these While reading this text, your eyes jump from word to cells part of the putative where pathway, they also carry word. Yet you are unaware of the motion this causes information on eye position and those in LIP show sacon your retina; the brain somehow compensates for cade-related activity: all properties that, intuitively, these displacements and creates a stable percept of seem to be related to perisaccadic position perception. the world. This compensation is not perfect; perisac-If the neurons we recorded from are truly part of a cadically, perceptual space is distorted. We show that where pathway, it should be possible for an ideal obthis distortion can be traced to a representation of server to interpret their spikes in terms of the spatial retinal position in the medial temporal and medial sulocation of a stimulus. Our analysis finds an interpretaperior temporal areas. These cells accurately repretion of a neuron's firing rates that an ideal observer can sent retinal position during fixation, but perisaccadiuse to extract position information. This interpretationcally, the same cells distort the representation of called a codebook-explicitly links neural firing to the space. The time course and magnitude of this distorpercept an ideal observer would have. Our working hytion are similar to the mislocalization found psychopothesis is that mislocalization occurs around the time physically in humans. This challenges the assumption of saccades because the neurons that represent posiin many psychophysical studies that the perisaccadic tion during normal operation are in some, as yet unspeciretinal position signal is veridical. fied, manner "disturbed" by the imminent saccade. A downstream area, modeled here by the ideal observer,