Orientational specificity of line interactions in eccentric vision

In eccentric vision a stimulus letter presented singly is better recognisable than a stimulus letter which is flanked by other letters (Mackworth, 1965; Bouma 1969, 1970). This adverse interaction between letter stimuli was found to operate over relatively large visual angles P between test letter and flanking letters, Pm being about 0.5 ¢ (where Pm is the maximum value of P, and ¢ is the eccentricity of the testletter). Furthermore, indications were found (Bouma, unpublished) that this interaction might depend on similarities in shape between testletter and flanking letters. These findings gave rise to a further investigation of the nature of interactions in eccentric form recognition. Here we present evidence for the subjoined conclusions. Interactions in eccentric vision are not restricted to letter stimuli; they may also be found with much simpler forms, such as line-segments (figs. la and lb). One of the factors involved in interactions between line-segments is the difference in orientation between test stimulus and interaction stimulus. The ratio Pm/¢ that can be found for equally orientated same order as that found in letter interaction.