Research Report Classification images of two right hemisphere patients: A window into the attentional mechanisms of spatial neglect Steven Shimozaki a, ⁎ , Alan Kingstone b , Bettina Olk c , Robert Stowe d , Miguel Eckstein a a Department of Psychology, University of California, Santa Barbara, CA 93106, USA b Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada c School of Humanities and Social Sciences, International University Bremen, Bremen, Germany d Departments of Psychiatry and Neurology, University of British Columbia School of Medicine and Riverview Hospital, Canada ARTICLE INFO ABSTRACT Article history: Accepted 9 January 2006 Available online 21 February 2006 While spatial neglect most commonly occurs after right hemisphere lesions, damage to diverse areas within the right hemisphere may lead to neglect, possibly through different mechanisms. To identify potentially different causes of neglect, the visual information used (the ‘perceptual template’) in a cueing task was estimated with a novel technique known as ‘classification images’ for five normal observers and two male patients with right- hemisphere lesions and previous histories of spatial neglect (CM, age 85; HL, age 69). Observers made a yes/no decision on the presence of a ‘White X’ checkerboard signal (1.5°) at one of two locations, with trial-to-trial stimulus noise added to the 9 checkerboard squares. Prior to the stimulus, a peripheral precue (140 ms) indicated the signal location with 80% validity. The cueing effects and estimated perceptual templates for the normal observers showed no visual field differences. Consistent with previous studies of spatial neglect, both patients had difficulty with left (contralesional) signals when preceded by a right (ipsilesional) cue. Despite similar behavioral results, the patients' estimated perceptual templates in the left field suggested two different types of attentional deficits. For CM, the left template matched the signal with left-sided cues but was opposite in sign to the signal with right-sided cues, suggesting a severely disrupted selective attentional strategy. For HL, the left templates indicated a general uncertainty in localizing the signal regardless of the cue's field. In conclusion, the classification images suggested different underlying mechanisms of neglect for these two patients with similar behavioral results and hold promise in further elucidating the underlying attentional mechanisms of spatial neglect. © 2006 Elsevier B.V. All rights reserved. Keywords: Visual attention Spatial neglect Cueing Classification image Bayesian observer 1. Introduction 1.1. Spatial neglect and cueing Spatial neglect can occur after a unilateral brain injury and describes a syndrome in which the patient ignores visual information in the hemifield opposite to the side of the lesion (for a review, see Rafal, 1994; Lezak, 1995; Gazzaniga, 1998). It is not a purely visual deficit as it can be dissociated from visual field loss (hemianopia), and it is commonly assumed that hemineglect reflects an attentional deficit (although many have argued that hemineglect also reflects a deficit in the BRAIN RESEARCH 1080 (2006) 26 – 52 ⁎ Corresponding author. Fax: +1 805 893 4303. E-mail address: shimozak@psych.ucsb.edu (S. Shimozaki). URL: http://www.psych.ucsb.edu/~eckstein/lab/steve5.html (S. Shimozaki). 0006-8993/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2006.01.033 available at www.sciencedirect.com www.elsevier.com/locate/brainres