Influence of unattended features on the processing of a single line segment.

This work investigates the interference of unattended line segments (distractors) of different orientations on a single line segment (target) when observer attention is focused on it in order to determine its orientation. It appears that the presence of line segments of different orientations in the visual field strongly influences the observer's decision on the judgement of the target orientation, whereas sensitivity is not affected. Two experiments were carried out to investigate distractor influence as a function of their number (Experiment I) and as a function of their proximity to the target, that is, to the point on which attention is focused (Experiment II). It appeared that distractors close to the target interfered more intensely than distractors at greater distances from the target, even if the latter were far more numerous. The results suggest that the output of the decision system is a function of all the information transmitted by feature detectors which act separately and in parallel.