Intramanual and intermanual transfer of the curvature aftereffect

The existence and transfer of a haptic curvature aftereffect was investigated to obtain a greater insight into neural representation of shape. The haptic curvature aftereffect is the phenomenon whereby a flat surface is judged concave if the preceding touched stimulus was convex and vice versa. Single fingers were used to touch the subsequently presented stimuli. A substantial aftereffect was found when the adaptation surface and the test surface were touched by the same finger. Furthermore, a partial, but significant transfer of the aftereffect was demonstrated between fingers of the same hand and between fingers of both the hands. These results provide evidence that curvature information is not only represented at a level that is directly connected to the mechanoreceptors of individual fingers but is also represented at a stage in the somatosensory cortex shared by the fingers of both the hands

Retinotopic Mapping of Categorical and Coordinate Spatial Relation Processing in Early Visual Cortex

Spatial relations are commonly divided in two global classes. Categorical relations concern abstract relations which define areas of spatial equivalence, whereas coordinate relations are metric and concern exact distances. Categorical and coordinate relation processing are thought to rely on at least partially separate neurocognitive mechanisms, as reflected by differential lateralization patterns, in particular in the parietal cortex. In this study we address this textbook principle from a new angle. We studied retinotopic activation in early visual cortex, as a reflection of attentional distribution, in a spatial working memory task with either a categorical or a coordinate instruction. Participants were asked to memorize a dot position, with regard to a central cross, and to indicate whether a subsequent dot position matched the first dot position, either categorically (opposite quadrant of the cross) or coordinately (same distance to the centre of the cross). BOLD responses across the retinotopic maps of V1, V2, and V3 indicate that the spatial distribution of cortical activity was different for categorical and coordinate instructions throughout the retention interval; a more local focus was found during categorical processing, whereas focus was more global for coordinate processing. This effect was strongest for V3, approached significance in V2 and was absent in V1. Furthermore, during stimulus presentation the two instructions led to different levels of activation in V3 during stimulus encoding; a stronger increase in activity was found for categorical processing. Together this is the first demonstration that instructions for specific types of spatial relations may yield distinct attentional patterns which are already reflected in activity early in the visual cortex

All elements of the trialsequence: an interval (10000 ms), first stimulus presentation (300 ms), jittered interval (3000–8000 ms), second stimulus presentation (300 ms), and a fixation cross during which a response could be given (2000 ms).

<p>All elements of the trialsequence: an interval (10000 ms), first stimulus presentation (300 ms), jittered interval (3000–8000 ms), second stimulus presentation (300 ms), and a fixation cross during which a response could be given (2000 ms).</p

Schematics of the stimuli used for mapping.

<p>A) A clockwise rotating wedge for polar angle mapping. B) An expanding circle for eccentricity mapping. Arrows are for illustration purposes only.</p

Mean regression coefficients related to all three stimulus types for A) V1, B) V2, and C) V3.

<p>Means are presented for both the categorical (cat) and coordinate instruction (coo) as well as the first stimulus (S1), the matching region of the second stimulus (S2 match), and the mismatching region of the second stimulus (S2 mismatch). Error bars represent the standard error of the mean (SEM).</p

The cross dot stimulus with all possible dot positions.

<p>The central cross was red in all first stimuli (S1) and green in all second stimuli (S2). Note that only one of these dots was present in a single stimulus.</p

Mean accuracy (Acc) and response times (RT) for both the categorical and coordinate condition.

<p>Standard deviation in parentheses.</p

Mean regression coefficients of the retention interval between the first and second stimulus for A) V1, B) V2, and C) V3.

<p>Means are presented for both the categorical (cat) and coordinate instruction (coo) as well as the regions that would match and mismatch in comparison to the first stimulus. Error bars represent the standard error of the mean (SEM).</p