Neglect determined by the relative location of responses.

Abstract

The aim of the present study was to assess the relevance of relative position coding of the effectors in the determination of neglect for the space of response. Two groups of patients were selected: an experimental group, consisting of right brain-damaged patients with left unilateral neglect, and a control group, consisting of right brain-damaged patients without unilateral neglect. These patients participated in two different experiments. In Experiment 1 the stimuli were horizontally aligned to the left and the right of a fixation stimulus; in Experiment 2 they were vertically aligned above and below the fixation stimulus. The stimuli consisted either of the number '1' or the number '2'. In both experiments, the patient was required to give a relative left key press response upon presentation of number '1' and a relative right key press response upon presentation of number '2'. The responses were recorded using the index and middle fingers of the right hand and the response keyboard was located on the right side of body midline. In each experiment there were two hand response conditions: standard and reversed. Under the former condition the hand was in the normal upright position; under the latter, the hand and the response keyboard were rotated by approximately 180 degrees. Under the standard condition, the two effectors were located on the typical anatomical spatial position, i.e. the index finger, which was located on the left relative position, pressed the left key, and the middle finger, which was located on the right relative position, pressed the right key. Under the reversed condition, the positions of the two effectors were reversed, i.e. the middle finger located on the left relative spatial position pressed the left key and the index finger, located on the right relative spatial position, pressed the right key. The results for both experiments showed that neglect patients were always slower to respond when the task required a left key response. The effect was manifest under both the standard and the reversed conditions. The neglect was therefore for the space of response and not for the anatomical spatial position of the effectors.