Dorsal stream contributions to perceptual asymmetries

Evidence for abnormal visuospatial attentional processes in the interictal migraineur

Research shows decreased brain region activity in the right temporo-parietal junction (rTPJ) in people with migraine headache relative to headache-free controls when performing an orienting visuospatial attention task. Functional inactivation of the rTPJ has been associated with rightward performance deviations on laterality-based attention Landmark (LM) and greyscale (GRE) tasks in individuals with unilateral neglect and heightened activation in the rTPJ is associated with leftward deviation, known as pseudoneglect, in controls on these tasks. Given this, we investigated whether migraineurs would lack the leftward deviation found in headache-free controls on visuospatial attention tasks. 36 migraineurs and 38 controls were presented with LM and GRE tasks. Response bias scores showed a significant difference in responses between groups (p = 0.036) on the GRE, a luminance-based task, but not on the LM, a size-based task (p = 0.826). This study is the first to show laterality-based attentional differences in migraineurs, as compared to controls. Specifically, migraineurs were found to have smaller leftward biases on luminance-based visuospatial attention tasks, as compared to controls, aligning with previous research suggesting that migraine may be having an impact on a variety of attention tasks in migraineurs in between headache attacks.

Through Doorways and Down Corridors: Investigating Asymmetries During Computer Maze Navigation

Pseudoneglect causes neurologically intact individuals to bias their attention to the left in near space, and to the right in far space. These attentional asymmetries impact both ambulatory and non-ambulatory activities, causing individuals to deviate rightward. While most studies investigating real-world navigation have found a rightward deviation when passing through a door, some have found the opposite pattern for corridors. To explore this dissociation, the current experiment explicitly compared navigation through doorways and corridors. To allow for a direct comparison between these two environments, the navigation task was undertaken in a simulated environment. Dextral participants (n = 98) completed several trials in either the doorway or corridor condition and their mean lateral position and variance was analysed. A rightward deviation was observed for doorways, consistent with previous research. Rightward biases were also observed for corridors, irrespective of the position within the corridor. The results argue against an explanation based on near/far space for the leftward bias in corridors. An explanation based on elevation of view is proposed as an alternative. The study also demonstrates that simulated environments provide an efficient means of investigating asymmetries in navigation.

Looking up improves performance in verbal tasks

Earlier research suggested that gaze direction has an impact on cognitive processing. It is likely that horizontal gaze direction increases activation in specific areas of the contralateral cerebral hemisphere. Consistent with the lateralization of memory functions, we previously showed that shifting gaze to the left improves visuo-spatial short-term memory. In the current study, we investigated the effect of unilateral gaze on verbal processing. We expected better performance with gaze directed to the right because language is lateralized in the left hemisphere. Also, an advantage of gaze directed upward was expected because local processing and object recognition are facilitated in the upper visual field. Observers directed their gaze at one of the corners of the computer screen while they performed lexical decision, grammatical gender and semantic discrimination tasks. Contrary to expectations, we did not observe performance differences between gaze directed to the left or right, which is consistent with the inconsistent literature on horizontal asymmetries with verbal tasks. However, RTs were shorter when observers looked at words in the upper compared to the lower part of the screen, suggesting that looking upwards enhances verbal processing.