Example of the greyscales stimuli. When asked to indicate which stimulus is darker overall, participants typically select the stimulus that is dark on the left-hand side. This bias occurs despite the fact that the stimuli are equiluminant.

Example of the greyscales stimuli. When asked to indicate which stimulus is darker overall, participants typically select the stimulus that is dark on the left-hand side. This bias occurs despite the fact that the stimuli are equiluminant.

Visual Assymetries

Damage to the right hemisphere, especially the parietal regions can result in a disorder known as spatial neglect. This disorder causes individuals to over-attend to their right side and to neglect the left.

While many people are aware of the extreme rightward bias that occurs in neglect, fewer are aware of the leftward attentional bias that occurs in normally functioning individuals. This bias, also known as pseudoneglect, causes people to bisect lines slightly to the left of their true centre. Our current research programme aims to uncover the cognitive and neurological mechanisms that underlie pseudoneglect.

Pseudoneglect is indexed with the greyscales task. An example of the task is shown in figure below. When asked to indicate which image appears darker overall, participants will typically pick the stimulus that is darker on the left side, irrespective of whether it is on the top or bottom. Normal participants show a robust preference of approximately 65% for the leftward stimulus. In contrast, neglect patients show an extreme bias in the opposite direction and will pick the stimulus that is dark on the right over 90% of the time. Even when patients with right parietal damage have recovered and show no obvious sign of neglect for cancellation and line bisection tasks, a rightward bias is found for the greyscales task.

Researchers

 Daniel Carragher, Mike Nicholls

External collaborators

Nicole Thomas

Publications

Okubo, M., & Nicholls M. E. R. (in press). A stimulus-dependent dissociation between the cerebral hemispheres under free-viewing conditions. Experimental Brain Research.

Nicholls, M. E. R., Smith, A., Mattingley, J. B., & Bradshaw, J. L. (in press). The effect of body and environment-centred coordinates on free-viewing perceptual asymmetries for vertical and horizontal stimuli. Cortex.

Nicholls, M. E. R., Mattingley, J. B., & Bradshaw, J. L. (2005). The effect of strategy on pseudoneglect for luminance judgements. Cognitive Brain Research25, 71-77.

Orr, C. A., & Nicholls, M. E. R. (2005). The Nature and Contribution of Space- and Object-Based Attentional Biases to Free-Viewing Perceptual Asymmetries. Experimental Brain Research162, 384-393.

Nicholls, M. E. R., Mattingley, J. B., Berberovic, N., Smith, A., & Bradshaw, J. L. (2004). An investigation of the relationship between free-viewing perceptual asymmetries for vertical and horizontal stimuli. Cognitive Brain Research19, 289-301.

Nicholls, M. E. R., Hughes, G., Mattingley, J. B., & Bradshaw, J. L. (2004). Are object and space-based attentional biases both important to free-viewing perceptual asymmetries? Experimental Brain Research154, 513-520.

Mattingley, J. B., Berberovic, N., Corben, L., Slavin, M. J., Nicholls, M. E. R., & Bradshaw, J. L. (2003). The greyscales task: a perceptual measure of attentional bias following right hemisphere damage. Neuropsychologia42, 387-394.

Nicholls, M. E. R., Mattingley, J. B., Bradshaw, J. L., & Krins, P. (2003). Trunk- and head-centred spatial coordinates do not affect free-viewing perceptual asymmetries. Brain & Cognition53, 247-252.

Nicholls, M. E. R., & Roberts, G. R. (2002). Pseudoneglect: a scanning, pre-motor or attentional bias? Cortex38, 113-136.

Nicholls, M. E. R., Bradshaw, J. L., & Mattingley, J. B. (2001). Unilateral hemispheric activation does not affect free-viewing perceptual asymmetries. Brain & Cognition, 46, 219-223.

Nicholls, M. E. R., Bradshaw, J. L., & Mattingley, J. B. (1999). Free-viewing perceptual asymmetries for the judgement of shade, numerosity and size. Neuropsychologia, 37, 307-314.