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| Cosimo Urgesi |
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Dip. di Psicologia, Via dei marsi 78 - 00185 Roma
e-mail: urgesi@tiscali.it |
Poster Presentation: |
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| Cerebral dominance and hemispheric metacontrol in normal subjects investigated by means of chimeric figures. |
| Urgesi Cosimo 1, Boscaglia Chiara 1, Bricolo Emanuela 2, Aglioti Salvatore M. 1,3 | |
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1. Department of Psychology, University of Rome \"La Sapienza\", Roma
2. Dipartimento di Psicologia, Edificio U6 , Universitŕ degli Studi di Milano-Bicocca
3. Centro Ricerche di Neuropsicologia IRCCS Fondazione Santa Lucia, Via Ardeatina, Roma |
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| Interhemispheric integration and hemispheric metacontrol were investigated by testing the ability of 55 normal subjects to match tachistoscopically presented chimeric or normal faces with one out of four normal face stimuli presented in free vision. Trials with half-faces were also used. The two half-stimuli of chimerics and wholesome faces were presented simultaneously (exposure time: 10, 20, 30, 40 or 50 ms) or asynchronously (stimulus onset asynchrony: 10, 20, 30, 40 or 50 ms). While subjects were informed that half faces could be presented, no mention to the presence of chimerics was made. In Experiment 1 verbal and non-verbal responses were requested in separate blocks of trials; in Experiment 2 and 3 subjects responded by pressing one key corresponding to one of the four probe stimuli. Subjects did not detect consciously the presence of chimeric stimuli for simultaneous presentations lasting up to 40 ms. However, performance in matching at least one half of the chimerics was poorer than for entire stimuli, both in accuracy and RTs. Moreover, an improvement of performance contingent upon the increase of exposure time was parallel for chimeric and wholesome faces thus hinting at an implicit processing of chimerics. The asynchronous presentation of the two hemi-figures induced the capability of detecting the presence of chimeric stimuli when the compounding half-stimuli were separated in time thus indicating that the suppression of conflicts between the two parts of chimeric stimuli occurred only when the compounding parts were together on the screen. Although the modality of response did not determine a dynamic shift of hemispheric dominance, a superiority of the right hemisphere in the face recognition task was found in our study. The preference for choosing the probe stimulus corresponding to the left half-face of chimerics disappeared when subjects learned the names associated to the faces and when the left hemi-field was stimulated first. While the right hemisphere dominance was influenced by task variables, the level of performance always reflected the right hemisphere specialization in face recognition. Thus, the dissociation between hemispheric dominance and specialization hints at the existence of hemispheric metacontrol in normal subjects. |
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