Frequency of seeing and radial localization of single and multiple visual stimuli.

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Abstract
Single and multiple stimuli were presented on the circumference of an imaginary circle for various luminance-duration combinations. The Ss estimated the radial position of the stimulus or stimuli which varied in number from one through seven. The data indicate that radial localization accuracy is independent of the variables of luminance and duration, provided the stimulus or stimuli are visible. With an increase in the number of stimuli presented the radial localization error per stimulus increases. The error function increases rapidly at first with an increase in the number of stimuli, and then more slowly, before approaching a limiting value. The assumption by Schlosberg that the perception of a stimulus is an independent event was found to hold for a .32 mL-.01-sec. combination but not for a 5.12mL-.64 sec. combination. In the former case, the assumption that the probability of detecting exactly N stimuli is the nth power of the probability of seeing one stimulus was in good agreement with the data for 2,3 and 4 stimuli but overestimated the results for 5,6, and 7 stimuli. It is concluded that the mechanism of localization is not limited by the magnitude of the primary excitation process, the latter being completed before the localization mechanism is operative. No explanation is suggested for the observed increase in the localization error per stimulus as a function of the number of stimuli presented.

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