[show abstract][hide abstract] ABSTRACT: In this study, we investigated when visual perception begins in fixations. During picture viewing, the picture was degraded at the beginning of selected saccades and changed back to the original after varying intervals. Participants manually responded whenever they detected changes. The change-backs were undetected when they occurred <6 msec after the end of the saccade, marked by the peak of the overshoot in dual Purkinje image eyetracker data, and detection reached asymptote 32 msec after that marker. Eye velocity at the change-back time also affected detection likelihood. Apparently, perception begins around the time at which the eyes stop rotating at the end of a saccade, giving a psychological justification for measuring fixation durations from then. This also specifies the deadline for gaze-contingent display changes to occur without detectable image motion. Investigators using the dual Purkinje image eyetracker should consider the peak of the overshoot as the fixation onset time and measure intrafixational presentation times from then.
Behavior research methods, instruments, & computers: a journal of the Psychonomic Society, Inc 12/2002; 34(4):481-90.
[show abstract][hide abstract] ABSTRACT: Visually evoked potentials (VEP) and reaction time (RT) were recorded under stimulation with sinusoidal gratings. Grating spatial frequency (SF) was 0.5, 5 or 12 cd and grating contrast was varied. Consistent with previous findings, both VEP latency and RT increased with the increase of grating SF and with the decrease of grating contrast. It was found, in addition, that RT and VEP latency increased by approximately the same amount when SF increased from 0.5 to 5 cd, thus suggesting that the main source of the RT delay at 5 cd in comparison with RT at 0.5 cd is of peripheral origin. However, in comparison with the data at 0.5 and 5 cd, RT at 12 cd increased much more than VEP latency. We conclude that the RT delay at high SF involves a substantial central component in addition to the peripheral delay.
Vision Research 03/1999; 39(4):699-705. · 2.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The influence of the spatial frequency of visual stimuli on hemispheric asymmetry has been studied with visual evoked potentials (VEP). Nineteen different sinusoidal gratings (19 SF from 1 to 10 cpd) were presented in an ON-OFF mode to five right-handed subjects. The amplitude of the VEPs and the latency of the first positive component (C1) were analyzed. The results show that in the low range of spatial frequencies, the latency and the amplitude of C1 are similar in both hemispheres. At medium to high spatial frequencies, the VEPs on the right hemisphere (RH) present shorter latencies and larger amplitudes than those on the left hemisphere (LH). These results, discussed in relation to the directional differences in the time of callosal interhemispheric transfer, strengthen the idea that the RH is relatively more sensitive than the LH to the spatial component of the visual stimuli.
Brain and Cognition 02/1998; 36(1):21-9. · 2.82 Impact Factor
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