Rightward biases in free-viewing visual bisection tasks: Implications for leftward responses biases on similar tasks Lorin J. Elias * , Brent Robinson, Deborah M. Saucier Department of Psychology, University of Saskatchewan, 9 Campus Drive, Saskatoon, Sask., Canada S7N 5A5 Accepted 12 February 2004 Abstract Neurologically normal individuals exhibit strong leftward response biases during free-viewing perceptual judgments of bright- ness, quantity, and size. When participants view two mirror-reversed objects and they are forced to choose which object appears darker, more numerous, or larger, the stimulus with the relevant feature on the left side is chosen 60–75% of the time. This effect could be influenced by inaccurate judgments of the true centre-point of the objects being compared. In order to test this possibility, 10 participants completed three visual bisection tasks on stimuli known to elicit strong leftward response biases. Participants were monitored using a remote eye-tracking device and instructed to stare at the subjective midpoint of objects presented on a computer screen. Although it was predicted that bisection errors would deviate to the left of centre (as is the case in the line bisection liter- ature), the opposite effect was found. Significant rightward bisection errors were evident on two of the three tasks, and the leftward biases seen during forced-choice tasks could be the result of misjudgments to the right of centre on these same tasks. Ó 2005 Published by Elsevier Inc. Keywords: Pseudoneglect; Laterality; Attention; Bisection 1. Introduction Neurologically normal individuals bisect lines to the left of true centre (Jewell, 2000, #2), a phenomenon now referred to as pseudoneglect. However, there are other more obscure tasks that appear to demonstrate highly significant and reliable perceptual asymmetries. For instance, Mattingley, Bradshaw, Nettleton, and Bradshaw (1994) developed a task wherein two left/right reversed luminance gradients that changed from black to white were presented and neurologically normal par- ticipants were to indicate which side appeared to be dar- ker. The participants exhibited a strong leftward bias, usually choosing the gradient with the darkest end on the left side. This result was later replicated and extended by Nich- olls, Bradshaw, and Mattingley (1999) who presented left/right reversed greyscales, gradients of small stars, or shapes changing in size from one side to another. For the greyscales task, Nicholls et al. (1999) asked the participants to indicate which side was darker or lighter. For the gradients of small stars, participants were to indicate which side contained more or less stars. For the shape task, participants were asked to indicate which shape was larger or smaller. Regardless of the type of stimulus presented or the type of assessment being made, participants exhibited large leftward biases in their responding. The relationship between the leftward biases elicited by these three tasks and the pseudoneglect evident when normals complete line bisection tasks is unclear. When the same participants perform both types of tasks, there is a weak positive correlation (that approaches statistical significance) between the biases on the tasks (Nicholls & www.elsevier.com/locate/b&c Brain and Cognition 59 (2005) 296–298 0278-2626/$ - see front matter Ó 2005 Published by Elsevier Inc. doi:10.1016/j.bandc.2004.02.021 * Corresponding author. Fax: +1 306 966 6630. E-mail address: lorin.elias@usask.ca (L.J. Elias).