Concurrent processing of faces and speech in relation to hemispheric lateralization

In recognition of the ecological importance of the talking face and its potential role in the development of hemispheric lateralization, descriptive studies were undertaken to examine the effects of concurrent face and speech processing on hemispheric lateralization.; In Study 1, four faces were presented in tachistoscopic fashion via computer. Responses were 366 msec faster in the right hemisphere. The majority of subjects exhibited a right hemisphere processing speed advantage, but those who were relatively faster in the left hemisphere were more accurate.; In Study 2, a spoken word was incidentally presented concurrently with each face to simulate bimodal recognition of an individual. With concurrent processing of faces and related speech, the right hemisphere speed advantage disappeared and the group that was faster in the left hemisphere was no longer superior on face recognition. However, this group was superior on speech recognition. There were positive correlations between face and speech recognition performance for both hemispheres.; The third study examined the effects of having particular relationships between the faces and speech. Presenting unrelated speech with faces had the same effects on hemispheric advantage as presenting related speech. However, right hemisphere face recognition was no longer positively correlated with speech recognition. Observations suggesting a trade off in attention between faces and speech, for only the right hemisphere, are discussed.; Speech and face recognition performance for Studies 2 and 3 unexpectedly indicated that subjects did "two things at once"; even though, the speech was incidentally presented. This finding was explored in the final two studies. It was hypothesized that the special nature of the face speech combination was responsible. Processing of the non-ecological combination of silent inverted faces and inverted faces with speech was tested and provided no evidence for this hypothesis.; Two methodological issues were raised by these studies. When faces were inverted with task difficulty adjusted, there was no indication of a typically reported unequal decline in right hemisphere performance suggesting a confound in the face inversion literature between task complexity and inversion. Secondly, use of both reaction time and accuracy as measures of lateralization resulted in a number of disassociations between them suggesting that inferring equivalent advantages from these two measures is unwarranted.