Hemiface Contributions to Hemispheric Dominance in Visual Speech Perception Timothy R. Jordan University of Leicester Sharon M. Thomas Medical Research Council Institute of Hearing Research Lateralized displays are used widely to investigate hemispheric asymmetry in language perception. However, few studies have used lateralized displays to investigate hemispheric asymmetry in visual speech perception, and those that have yielded mixed results. This issue was investigated in the current study by presenting visual speech to either the left hemisphere (LH) or the right hemisphere (RH) using the face as recorded (normal), a mirror image of the normal face (reversed), and chimeric displays constructed by duplicating and reversing just one hemiface (left or right) to form symmetrical images (left-duplicated, right-duplicated). The projection of displays to each hemisphere was controlled precisely by an automated eye-tracking technique. Visual speech perception showed the same, clear LH advantage for normal and reversed displays, a greater LH advantage for right-duplicated displays, and no hemi- spheric difference for left-duplicated displays. Of particular note is that perception of LH displays was affected greatly by the presence of right-hemiface information, whereas perception of RH displays was unaffected by changes in hemiface content. Thus, when investigated under precise viewing conditions, the indications are not only that the dominant processes of visual speech perception are located in the LH but that these processes are uniquely sensitive to right-hemiface information. Keywords: visual speech, laterality, hemispheric dominance, face perception The anatomy of the human visual system is such that nerve fibers carrying information about stimuli falling in the left visual hemifield project to the right hemisphere (RH), and fibers carrying information about stimuli falling in the right visual hemifield project to the left hemisphere (LH). Thus, under appropriate view- ing conditions, stimuli can be presented to whichever hemisphere is chosen by the experimenter. 1 Numerous studies have used this procedure to compare the linguistic abilities of the LH and RH. For example, a widely reported finding is that printed words are processed more effi- ciently when projected to the LH than to the RH (for overviews, see Bradshaw & Nettleton, 1983; Chiarello, 1988; Hellige, 1993), and there seems little doubt that this LH advantage reflects privi- leged access to specialized LH processing of linguistic information (e.g., Bub & Lewine, 1988; Jordan & Patching, 2003a, 2003b; Jordan, Patching, & Milner, 1998, 2000; Jordan, Patching, & Thomas, 2003a, 2003b; Jordan, Redwood, & Patching, 2003; Reuter-Lorenz & Baynes, 1992; Tarkiainen, Helenius, Hansen, Cornelissen, & Salmelin, 1999). However, it is far from clear that all visible language produces this pattern of hemispheric asymme- try with lateralized displays. Visible facial movements naturally accompany the production of auditory speech, and studies using centralized (i.e., non-later- alized) displays of speaking faces have shown that observers can identify silently spoken words from the visible facial movements made by a speaker (visual speech), and that these visible move- ments can increase the intelligibility of speech sounds across a range of viewing conditions (e.g., Arnold & Hill, 2001; Jordan & Bevan, 1997; Jordan & Thomas, 2001; MacLeod & Summerfield, 1990; Middleweerd & Plomp, 1987; Sumby & Pollack, 1954; Thomas & Jordan, 2004). However, despite the ubiquity of visual speech in human interaction, few studies have attempted to assess the perception of this particular type of visible language in later- alized displays. Those that have used a variety of approaches and present a mixed picture. Campbell (1986) presented silent unilateral displays of a per- son’s static face pronouncing a syllable, and participants indicated whether this visual syllable matched a previously presented audi- tory syllable. Participants responded faster when visual stimuli were projected to the RH than to the LH, suggesting RH domi- nance for visual speech perception. In contrast, Smeele, Massaro, Cohen, and Sittig (1998) presented silent unilateral displays of dynamic visual speech and found that visual speech was identified more accurately when projected to the LH, suggesting LH domi- nance for visual speech perception (see also Campbell, De Gelder, & De Haan, 1996). LH dominance for visual speech perception is also suggested by other, neuropsychological studies. Campbell and colleagues (Campbell, 1987; Campbell et al., 1990; Campbell, 1 In this article, when we refer to stimuli presented to one hemisphere in a divided field task, we are identifying the hemisphere that received the stimulus initially. Thus, in line with the logic of this technique, we do not assume that only one hemisphere has access to this information but that participants should show a performance advantage if the hemisphere that processes the stimulus more effectively receives the stimulus initially. Timothy R. Jordan, School of Psychology, Faculty of Medicine and Biological Sciences, Henry Wellcome Building, University of Leicester, Leicester LE1 9HN, United Kingdom; Sharon M. Thomas, Medical Re- search Council Institute of Hearing Research, University Park, Nottingham NG7 2RD, United Kingdom. Correspondence concerning this article should be addressed to Timothy R. Jordan, School of Psychology, Faculty of Medicine and Biological Sciences, Henry Wellcome Building, University of Leicester, Leicester LE1 9HN, United Kingdom. E-mail: Prof.TimJordan@leicester.ac.uk Neuropsychology Copyright 2007 by the American Psychological Association 2007, Vol. 21, No. 6, 721–731 0894-4105/07/$12.00 DOI: 10.1037/0894-4105.21.6.721 721