Context dependence in visual feature processing

Dependence in visual feature processing was studied with two identification experiments using briefly exposed stimuli. The basic stimuli consisted of two orthogonal line segments which formed either one of the four angles of a square, and the subject had to identify the location of the horizontal and vertical line segment making up a stimulus. In the first experiment, the two orthogonal line segments were sometimes separated by a gap. In the second experiment, either a 45° diagonal or a 135° diagonal or both were added to the right angles. With the observed response frequencies two forms of independence in feature detection were tested. Feature detection is called state independent if the detection of a feature is independent of the detection of another feature. According to context independence the detection of a feature is independent of the orientation and location of other features in the stimulus. Feature detection was shown to be context dependent whereas the hypothesis of state independence was not rejected, and state independence was unrelated to the size of the gap between the two orthogonal line segments in the first experiment. It was argued that the context effects obtained (context dependence) had occurred early in processing during the automatic activation of representational units corresponding to features before controlled search, interpretation and decision processes became involved.