The influence of stimulus orientation on the vertex positive scalp potential evoked by faces
- 107 Downloads
The scalp-recorded “vertex-positive peak” (VPP) evoked by images of faces in humans has previously been shown to be delayed when an originally upright stimulus is inverted or rotated by 90° (Jeffreys 1989a). This paper describes a study of the effects on this scalp potential of smaller face orientation changes (15° increments). The results showed that, under normal viewing conditions of clearly defined facial images, the VPP latency, which was minimal for face orientations within 15° of the vertical (0°), increased almost linearly for incremental rotations from 15 up to 90°, but was relatively unchanged or decreased slightly for further rotations from 90 up to 180°. Similar results were observed for clockwise and anticlockwise rotations, and for different facial representations. These stimulus orientation changes did not change the latency of simultaneously recorded, pattern-specific potentials recorded from occipital scalp locations; nor did they greatly affect the VPP amplitude. By contrast, rotations of “Mooney figure” stimuli away from the vertical produced concurrent reductions in both the perception of a face and the amplitude of the evoked VPP. Experiments in which the orientation of both the stimulus face and the subject's head were varied further showed that minimal latency VPP responses were evoked for parallel stimulus and viewing orientations. The speed of response is thus determined by the orientation of the subtended retinal image.
Key wordsVisual evoked potentials Face stimuli Stimulus orientation Humans
Unable to display preview. Download preview PDF.
- Grüsser O-J, Kirchhoff N, Naumann A (1990) Brain mechanisms for recognition of faces, facial expressions, and gestures: neuropsychological and electroencephalographic studies in normals, brain-lesioned patients, and schizophrenics. In: Cohen H, Bodis-Wollner I (eds) Vision and the brain. Raven, New York, pp 165–193Google Scholar
- Humphreys GW, Quinlan PT (1987) Normal and pathological processes in visual object constancy. In: Humphreys GW, Riddoch MJ (eds) Visual object processing: a cognitive neuropsychological approach. Erlbaum, Hilisdale, pp 43–105Google Scholar
- Jeffreys DA (1977) The physiological significance of pattern visual evoked potentials. In: Desmedt J (eds) Visual evoked potentials in man: new developments. Clarendon, Oxford, pp 134–167Google Scholar
- Jeffreys DA (1989b) Evoked potential studies of contour processing in human visual cortex. In: Kulikowski JJ, Dickinson CM, Murray IJ (eds) Contour and colour. Pergamon, London, pp 529–545Google Scholar
- Jeffreys DA, Tukmachi ESA (1991) Human scalp potentials evoked by face images of different orientation (abstract). J Physiol (Lond) 438:299PGoogle Scholar
- Rock I (1973) Orientation and form. Academic, New YorkGoogle Scholar
- Valentine T (1988) Upside-down faces: a review of the effects of inversion upon face recognition. Br J Psychol 81:141–145Google Scholar