April 6, 2007

Can blindsight lead to superior sight?

brain injury, perception, unconscious processes — thomasr

In a most interesting paper by Ceri Trevethan, Arash Sahraie and Larry Weiskrantz, it is suggested that blindsight patients are actually superior on certain visual stimulus detection tasks. In this paper, published in Cognition, the authors also provide experimental evidence that this is indeed the case.

The study highlights the neural dynamics that take place in the case of brain damage. While the areas that are damaged have been responsible for a given task (i.e. vision) it is likely that such injury leads to unmasking of previously suppressed functions in adjacent or other connected areas. As such, brain damage might indeed not only lead to reduced functions, but unmasking — and enhancement — of other functions. As in this study,

Can blindsight be superior to ‘sighted-sight’?

Ceri T. Trevethan, Arash Sahraie, and Larry Weiskrantz,

a: Vision Research Laboratories, School of Psychology, University of Aberdeen, Aberdeen, AB24 2UB Scotland, UK

Received 11 January 2006; revised 20 April 2006; accepted 21 April 2006. Available online 9 June 2006.


DB, the first blindsight case to be tested extensively (Weiskrantz, 1986) has demonstrated the ability to detect and discriminate a range of visual stimuli presented within his perimetrically blind visual field defect. In a temporal two alternative forced choice (2AFC) detection experiment we have investigated the limits of DB’s detection ability within his field defect. Blind field performance was compared to his sighted field performance and to an age-matched control group (n = 6). DB reliably detected the presence of a small (2°), low contrast (7%), 4.6 c/° Gabor patch with the same space-averaged luminance as the background presented within his blind field but performed at chance levels at the same eccentricity (11.3°) within his sighted field. Investigation of detection as a function of stimulus contrast revealed DB’s ability to detect the presence of an 8% contrast stimulus within his blind field, compared to 12% in his sighted field. No significant difference in detection performance between DB’s sighted field and the performance of six age-matched control participants suggests poor sighted field performance does not account for the results. Monocular testing also rules out differences between the eyes as an explanation, suggesting that DB demonstrates superior detection for certain stimuli within his visual field defect compared to normal vision.