Visual signal detection and lambda responses

On the basis of the result in earlier studies that the lambda response was associated with offset of the saccade, e.g., onset of the fixation pause, the relationship between the lambda response and the visual information processing load was examined. Eleven subjects were presented simultaneously random patterns including visual signals on Goldman perimeter and tone pips including auditory signals at random. In the visual task, the subject was instructed to search on the random pattern and detect the visual signals. In the auditory task, he was instructed to listen to tone pips without ceasing eye movements and detect the tone signals. EEGs from Oz and Cz, and the vertical and the horizontal EOGs were recorded. The vector EOG was calculated from both EOGs for detecting the absolute value of the saccade size. The occipital EEGs time-locked to offset of saccades were averaged 100 times to obtain lambda responses. The vertex EEGs time-locked to tone signals were averaged 100 times to obtain vertex potentials to auditory stimuli (AEP). Amplitudes of the lambda response (NOP100 and P100-N180) in the visual task were significantly higher than in the auditory task. Amplitudes of AEP (N1 and N1-P2) in the auditory task were enhanced significantly more than in the visual task. The results showed that the lambda response varied with information-processing load. The lambda response can be applicable as an index of visual information processing in eye movement situations.