68 A. Quayle et al. / Biological Psychology, 37 (1993) 43-71

Steady-state visually evoked potential topography and mental rotation

P. Line, R.B. Silberstein and A. Pipingas

Swinbume Centre for Applied Neurosciences Swinburne UniL;ersity of Technology, Hawthorn, WC 3122, Australia

Steady-state visually evoked potential (SSVEP) topography was examined in a complex mental rotation test (MRT). The SSVEP was recorded from 64 electrode sites using a multichannel electrode helmet, and elicited by a 13 Hz sinusoidal visual flicker, whilst the subjects performed a visual vigilance task and the MRT. Twenty male and 21 female right-handed subjects were used. In the MRT the subjects were required to choose the two figures which correctly matched the criterion figure in the centre. The figures were three- dimensional objects represented in two-dimensions on a computer screen. When compared with the visual vigilance task, the MRT was associated with SSVEP magnitude reductions in the frontal, occipito/ parietal and temporo/ parietal regions in the females and the frontal and occipito/parietal regions in the males. There were no consistent hemispheric differences in SSVEP magnitude. With SSVEP phase the males demonstrated the largest phase lag (increased latency) in the left temporo/parietal region and females in the right temporo/parietal region. Significance probability mapping, using the Hotelling’s T, found the temporo/parietal phase distribution suggests sex differences in the pattern of cortical activation associated with the MRT, but such a conclusion must be treated with caution as time variations in the SSVEP have not been considered.

ERP variability assessment in normal and epileptic subjects

A. Puce ‘, S.F. Berkovic ‘, P.J. Cadusch ’ and P.F. Bladin ’

’ Department of Medicine, UniL:ersity of Melbourne, Parkcille, VIC 3052, and Department of Neurology, Austin Hospital, Heidelberg, VIC 3084, Australia 2 Department of Physics, Swinburne University of Technology, Hawthorn, WC 3122, Australia

We compared P3 latency jitter in 13 subjects with temporal lobe epileps-. (TLE) with that of 13 normal controls. We predicted that increased jittt. would occur in TLE subjects, particularly on the epileptic side. Jitter was estimated using two methods: Woody’s algorithm and the maximum likeli- hood technique (MLT). The MLT is an iterative spectral estimation method