Current research interests

Free-viewing perceptual asymmetries

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.

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.

Publications produced by the laboratory in relation to this issue include:

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 Research 25, 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 Research.162, 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 Research 19, 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 Research. 154, 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. Neuropsychologia 42, 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 & Cognition 53, 247-252.

Nicholls, M.E.R. & Roberts, G.R. (2002). Pseudoneglect: a scanning, pre-motor or attentional bias? Cortex 38, 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.

Asymmetries in facial communication

The Mona Lisa (see figure below), like most painted portraits, turns her left cheek toward the artist so that the left side of her face is featured more than the right. This leftward bias is stronger for portraits of women than men and is not present for professional portraits. Our research suggests that the key factor underlying the bias is related to the desire to express emotion. The left side of the face, because it is controlled by the emotional right hemisphere, is more expressive of emotion. When individuals adopt an emotional role, or if they are emotionally expressive themselves, they are more likely to turn their left cheek when posing for a portrait. What's more, as observers, we find portraits that feature the left side of the face to be more emotionally expressive than those that feature the right.

Leonard da Vinci, c 1503. Mona Lisa

More recently, our research has examined the effect of emotional valence (happy - sad) on posing asymmetries. We found that portraits showing the right side are judged as happier whereas portraits featuring the left side of the face are judged to express sadness more strongly (see figure below). We have also begun to investigate facial asymmetries for the visual expression of speech. Our research in this area has demonstrated that the right side of the mouth is more important for lip-reading. This asymmetry is presumably brought about by the fact that the right side of the mouth is controlled by the left hemisphere, which is dominant for the production of speech.

Image captured using a 3-D range finding camera (Fiore) featuring either the (a) right or (b) left sides of the face. When asked to indicate which image looks happier, participants typically select the image featuring the right side of the face.

Publications produced by the laboratory in relation to this issue include:

Nicholls, M.E.R. & Searle, D.A. (In press). Asymmetries for the visual expression and perception of speech. Brain & Language.

Nicholls, M.E.R., Ellis, B.E., Clement, J. & Yoshino, M. (2004). Detecting hemifacial asymmetries in emotional expression with 3D computerised image analysis. Proceedings of the Royal Society 271, 663-668.

Nicholls, M.E.R., Searle, D & Bradshaw, J.L. (2004). Read my lips: Asymmetries in the visual expression and perception of speech revealed through the McGurk effect. Psychological Science 15, 138-141.

Nicholls, M.E.R., Clode, D., Lindell, A.K. & Wood, A.G. (2002). Which cheek to turn? The effect of gender and emotional expressivity on posing behaviour. Brain & Cognition 48, 480-484

Nicholls. M.E.R., Wolfgang, B.J., Clode, D. & Lindell, A.K. (2002). The effect of left and right poses on the expression of facial emotion. Neuropsychologia 40, 1662-1665.

Nicholls, M.E.R. (2000) Asymmetries in portraits: Insights from neuropsychology. In: M.K. Mandal, M.B. Bulman-Fleming & G. Tiwari (Eds). Side-bias: A neuropsychological perspective.. Kluwer Academic Publishers: Amsterdam.

Nicholls, M.E.R., Clode, D., Wood, S.J. and Wood, A, G. (1999). Laterality of expression in portraiture: Putting your best cheek forward. Proceedings of the Royal Society (section B) 266, 1517-1522.

Cerebral asymmetries in temporal processing

Traditionally, the functions of the left and right cerebral hemispheres have been described in relation to what material they process. For example, the left hemisphere is often described as 'verbal' whereas the right hemisphere is described as 'non-verbal' or 'spatial'. High-level descriptors, such as these, suffer from a lack of generality and fail to explain many phenomena associated with cerebral asymmetry. This laboratory has been involved with developing a new description of the hemispheres related to how material is processed.

Specifically, we have suggested that the left hemisphere is more efficient for processing information at a fast rate in a serial manner. The right hemisphere, in contrast, may be more efficient for processing information at a slower rate, and in parallel. A left hemisphere advantage for temporal processing may explain why the left hemisphere is better for tasks such as language production, speech comprehension and the control of fine movements - all of which require precise temporal control. Our laboratory has demonstrated a left hemisphere temporal processing advantage for a variety of tasks across the visual, auditory and tactile modalities.

Publications produced by the laboratory in relation to this issue include:

Okubo, M. & Nicholls, M.E.R. (2005). Hemispheric asymmetry in temporal resolution: Contribution of the magnocellular pathway. Psychonomic Bulletin & Review 12, 755-759.

Nicholls, M.E.R., Gora, J. & Stough C.K.K. (2002). Hemispheric asymmetries for visual and auditory temporal processing: An evoked potential study. International Journal of Psychophysiology 44, 37-55.

Kelso, W.M., Nicholls, M.E.R., Warne, G.L. & Zacharin, M. (2000). Cerebral lateralisation and cognitive function in patients with congenital adrenal hyperplasia (CAH). Neuropsychology 14, 370-378.

Nicholls, M.E.R. & Lindell, A. (2000). A left hemisphere, but not right hemispace, advantage for tactual simultaneity judgements. Perception & Psychophysics 62, 717-725.

Nicholls, M.E.R., Whelan, R.E. & Brown, S (1999). A left hemisphere temporal processing advantage for auditory and tactile stimuli. Brain & Cognition 40, 202-206.

Nicholls, M.E.R.,  Schier, M., Stough, C.K.K. & Box, A. (1999). Psychophysical and electrophysiological support for a left hemisphere temporal processing advantage. Neuropsychiatry, Neuropsychology and Behavioural Neurology 12, 11-16.

Nicholls, M.E.R. & Whelan, R.E. (1998). Hemispheric asymmetries for the temporal resolution of brief tactual stimuli. Journal of Clinical and Experimental Neuropsychology 20, 445-456.

Brown, S. & Nicholls, M.E.R. (1997). Hemispheric asymmetries for the temporal resolution of brief auditory stimuli. Perception and Psychophysics 59, 442-447.

Nicholls, M.E.R. (1996). Evidence and implications of a temporal processing dichotomy between the hemispheres. Laterality 1, 97-137.

Nicholls, M.E.R. (1994). Hemispheric asymmetries for temporal resolution: A signal detection analysis of threshold and bias. Quarterly Journal of Experimental Psychology 47a, 291-310

Nicholls, M.E.R. (1994). The non-contribution of attentional biases to visual field asymmetries for temporal discrimination. Neuropsychologia 32, 209-220.

Nicholls, M.E.R. and Atkinson, J. (1993). Hemispheric asymmetries for an inspection time task: A general left hemisphere temporal advantage? Neuropsychologia 31, 1181-1190.

Nicholls, M.E.R. and Cooper, C.J. (1991). Hemispheric differences in the rates of information processing for simple non-verbal stimuli. Neuropsychologia 29, 677-684.