Brief article Lapses of concentration and dyslexic performance on the Ternus task Chris Davis a, * , Anne Castles a,b , Ken McAnally a , Jacqueline Gray a a The University of Melbourne, Parkville, Victoria, Australia b Macquarie Centre for Cognitive Science, Macquarie University, Sydney, NSW, Australia Received 6 December 2000; accepted 12 January 2001 Abstract Recently, Cestnick and Coltheart (Cognition 71 (1999) 231) have reported evidence of abnormal performance on the Ternus apparent motion task in dyslexics. We demonstrate that some aspects of their data may be accounted for by more frequent lapses of concentration in the dyslexic group than in controls. We then report on a study in which a modi®cation of the Ternus procedure was employed to simplify the task and to control for the effects of inatten- tion. The results suggest that dyslexics do genuinely differ from normal readers in their perceptual processing. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Dyslexia; Ternus; Vigilance; Perceptual grouping; Magnocellular 1. Introduction A prominent theory of dyslexia is one based on low-level visual de®cits (e.g. Livingstone, Drislane, Rosen, & Galaburda, 1991; Lovegrove, 1996; Stein & Walsh, 1997). Speci®cally, it has been proposed that dyslexics have an impairment in the magnocellular system, one of two parallel, yet interconnected, visual pathways (Kaplan, Lee, & Shapley, 1990). As the magnocellular system is more sensitive to rapid changes than the companion parvocellular system (e.g. Merigan & Maun- C. Davis et al. / Cognition 81 (2001) B21±B31 B21 Cognition 81 (2001) B21±B31 www.elsevier.com/locate/cognit 0010-0277/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0010-0277(01)00129-9 COGNITION * Corresponding author. Department of Psychology, University of Melbourne, Parkville, VIC 3010, Australia. Fax: 161-3-9347-6618. E-mail address: cwd@unimelb.edu.au (C. Davis).