The effects of selective attention on chromatic processing; pattern-onset VEP responses
AuthorHighsmith, Jennifer Rea
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Intro: Electrophysiological and behavioral studies show that attention improves visual processing. Studies of chromatic steady-state and pattern-reversal visual evoked potentials (VEPs) support this. Typically in these studies VEP stimuli are displayed at one spatial location while distracter stimuli are displayed at a different spatial location. Waveform characteristics are shown to be attenuated when the VEP is unattended. More difficult distractor tasks have also shown to cause decrements in waveform characteristics. Typically, responses from extrastraite visual areas show robust effects with attentional modulations. Recording from lower visual areas such as V1 has not shown consistent attentional effects. Chromatic pattern-onset VEPs are thought to be low-level visual responses recorded over the primary occipital area. They have not been studied under conditions of selective attention. It is important to understand the effects of attentional shifts on the chromatic evoked potential because it has potential importance as a diagnostic tool in clinical settings where monitoring of attention can be difficult.Purpose: The present study measured the effects on the chromatic pattern-onset VEP with spatial and difficult, task-relevant attentional manipulations to show the sensitivity of this response to attentional shifts and the level of this response in the visual system. This study also aimed to determine if participant or patient monitoring is necessary when recording chromatic pattern-onset VEPs. Methods: Pattern stimuli were used to selectively activate the L-M and the S-(L+M) visual pathways. Waveform amplitudes and latencies were compared while attention was modulated with distractor tasks. In experiments one through four distractor stimuli were X's and O's presented out of synch with the VEP stimuli. In experiment one the VEP and distractor stimuli were spatially contiguous. In experiment two the VEP and distractor stimuli were spatially separated. In experiment three an achromatic pattern-reversal VEP was recorded with a spatially separate distractor. In experiment four VEP fixation was centrally located with the distractor presented in the periphery. In experiment five the VEP and distractor were presented in the same manner as experiment two, however the distractor was chromatic pattern-onset VEP stimuli identical to the recorded VEP stimuli but presented out of phase with the recorded stimuli. Results: Achromatic responses showed significant changes in amplitude and latency with attentional shifts. No significant changes were found for chromatic response in experiments one two, and four. In experiment five there was a marginally significant increase in amplitude for the VEP attention condition in the S-(L+M) pathway only. These results support the idea that chromatic pattern-onset responses may be low-level in the visual system. Additionally, for this response, it may not necessary to monitor attention in a laboratory or clinical setting.