Lateral masking in foveal and eccentric vision

Common to a number of investigations of visual letter recognition is the finding that adjacent letters interfere with the recognition of one another in eccentric vision (the non-central fovea and parafovea). This visual interference or lateral masking has been observed with letters forming words (Bouma, 1973; Shaw and Weigel, 1973) as well as in spaced arrays of various configurations (Anstis, 1974; Bouma, 1970; Eriksen and Rohrbaugh, 1970; Estes et al., 1976; Krumhansl and Thomas, 1977; Taylor and Brown, 1972; Wolford and Hollingsworth. 1974a. b); furthermore, besides being found in the more usual studies using recognition accuracy as the dependent variable, it also has been observed with reaction time being the dependent variable (Eriksen and Hoffman, 1972). along the abscissa of Fig. 1. Stimuli were made by applying contact letters (Helvetica 18 point; Chartpak M5218CL) and solid squares (Chartpak M452) to plain white index cards. one stimulus to a card All letters were 4.6 mm high and varied in width from 3.6 to 4.6 mm (mean = 3.9 mm); stroke width was nearly uniform at 0.5 mm. For the three surround conditions in order of increasing spacing, the separation between squares was 5.5, 8.7 and 17.1 mm. On a given trial. a single stimulus card was presented against a uniform white background of large dimensions. Luminance of the stimulus card as measured by Spectra Spotmeter was 28.1 cd/m* with the measured contrast of the letters and squares being 0.043.