Abstract:
The role of the dorsal and ventral visual streams in attentional orienting were examined in three experiments. The first a behavioural test, the second a high-density EEG, and the third a neuropsychological case study. Visual attention was examined by using peripheral cues that were either symbolic-semantic ‘identity’ or visuospatial ‘landmark’ cues to respond to a target. In experiment one, when cues were presented briefly (66ms), only landmark cues could facilitate the response time of locating a target. Identity cues were able to facilitate target detection only with a sustained cue presentation time of 133ms. This was interpreted in terms of the transient and sustained response characteristics of the dorsal M-cells and ventral streams P-cells respectively. The EEG showed stronger C1 waveforms for landmark cues in the parietal-occipital electrodes, overlaying dorsal areas (compared to the identity cues) and vice versa, the identity cues showed stronger waveforms in the temporo-occipital electrodes, overlaying ventral areas. The neuropsychological experiment showed a patient with a lesion in the dorsal area of the right parietal occipital junction, had a clear ability to use identity cues, but was unable to utilise landmark cues. This may be because of the damaged dorsal stream. Taken together these findings provide support for the unified model of vision and attention.
