Handedness and individual differences

Left-handers are thought to possess a number of special cognitive abilities: some of them good, some bad. Whether or not these differences in cognitive ability exist often goes to the heart of genetic models, which attempt to explain why left handedness exists. We have collected data from a number of sources to examine the relationship between handedness and factors such as cognitive ability and schizotypy. In general we find that left- and mixed-handers do worse overall. We also find that the lower levels of cognitive ability are not related to birth stress, which is one putative cause of left-handedness.

Our publications in this area include:

Chapman, H. L., Grimshaw, G. M., & Nicholls, M. E. R. (in press). Going beyond students: An association between mixed-hand preference and schizotypy subscales in a general population. Psychiatry Research.

Nicholls, M. E. R., Chapman, H .L., Loetscher, T., & Grimshaw, G. (2010). The relationship between hand preference, hand performance and general cognitive ability. Journal of the International Neuropsychological Society, 16, 585-592.

Johnston, D., Nicholls, M. E. R., Shaw, M., & Shields, M. (2009). Nature’s experiment? Handedness and early childhood development. Demography, 46, 281-301.

Nicholls, M. E. R., Orr, C. A., & Lindell, A. K. (2005). Magical ideation and its relation to lateral preference. Laterality, 10, 503-515.

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Numerical cognition and spatial attention

Besides their obvious arithmetic qualities, numbers can also have a spatial quality. Research demonstrates that, when we think about small or large numbers, our attention automatically shifts to the left or right sides of space, respectively. Our research has demonstrated that these shifts of attention are automatic and operate independently of motor responses. We have also demonstrated that attention can be shifted along the mental number using prismatic glasses and exogenous cues.

Our publications in this area include:

Nicholls, M. E. R., Lew, M., Loetscher, T., & Yates, M. J. (in press). The importance of response-type to the relationship between temporal order and numerical magnitude. Attention, Perception & Psychophysics.

Loetscher, T., Bockisch, C. J., Nicholls, M. E. R., & Brugger, P. (2010). Eye position predicts what number you have in mind. Current Biology, 20, 264-265.

Loetscher, T., Nicholls, M. E. R., Towse, J. N., Bradshaw, J. L., & Brugger, P. (2010). Lucky numbers: Spatial neglect affects physical, but not representational, choices in a Lotto task. Cortex, 46, 685-690.

Nicholls, M. E. R., & McIlroy, A. M. (2010). Spatial cues affect mental number line bisections. Experimental Psychology, 57, 315-319.

Jarick, M., Dixon, M. J., Maxwell, E. C., Nicholls, M. E. R., & Smilek, D. (2009). The Ups and Downs (and Lefts and Rights) of Synaesthetic Number Forms: Validation from Spatial Cueing and SNARC-Type Tasks. Cortex, 45, 1190-1199.

Loftus, A., Nicholls, M. E. R., Mattingley, J. B., Chapman, H. L., & Bradshaw, J. L. (2009). Pseudoneglect for the bisection of mental number lines. Quarterly Journal of Experimental Psychology, 62, 925-945.

Loftus, A. M., Vijayakumar, N., & Nicholls, M. E. R. (2009) Prism adaptation overcomes pseudoneglect for the greyscales task. Cortex, 45, 537-543.

Nicholls, M. E. R., Kamer, A., & Loftus, A. M. (2008). Pseudoneglect for mental alphabet lines is affected by prismatic adaptation. Experimental Brain Research, 191, 109-115.

Loftus, A. M., Nicholls, M. E. R., Mattingley, J. B., & Bradshaw, J. L. (2008). Numerical processing overcomes left neglect. Neuroreport, 19, 835-838.

Loftus, A. M., Nicholls, M. E. R., Mattingley, J. B., & Bradshaw, J. L. (2008). Left to right: Representational biases for numbers and the effect of visuomotor adaptation. Cognition, 107, 1048-1058

Nicholls, M. E. R., Loftus, A., & Gevers, W. (2008). Look, no hands: A perceptual task shows that number magnitude induces shifts of attention. Psychonomic Bulletin & Review, 15, 413-418.

Nicholls M. E. R., & Loftus, A. (2007). Pseudoneglect and neglect for mental alphabet lines. Brain Research, 1152, 130-138.

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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.

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

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