Inadequacies involved in the methodologies for studying rate of information processing in visual perception were discussed in terms of current models and knowledge of visual perception. A different methodology was introduced based on a 10-channel tachistoscope which permitted the presentation of letter stimuli at varying rates. The task was visual search with .9 required to detect whether an A (target) had occurred in a sequence of letters presented on a trial. Each letter was presented for approximately 2 msec, with the rate between letters varying from 5 msec, to approximately 3 sec. In addition to rate the number of letters presented in a trial (sequence length) and the location of the target in the sequence were studied. The only significant effect was the number of letters in a sequence. Detection sensitivity decreased with increasing sequence length. Control experiments indicated that this change in sensitivity was not attributable to an overloading of the encoding mechanism but rather was attributable to a change in the judgmental task. An increase in the number of noise letters disproportionately increased the number of false alarms relative to the hits. A simple probability model was able to describe the obtained results with fair accuracy. Presentation rate was immaterial. Detection was the same with only 5 msec, between letters in the sequence as with 3 sec. Failure to find a rate effect was interpreted in terms of filtering processes that operate in visual perception prior to the encoding process.The rate at which a human can process procity has been found to hold for temporal information in the visual channel would ap-durations of as much as 100 msec, or more pear at the first level of analysis to depend for perceived brightness, and recent work on the number of discrete percepts that he (Kahneman, 1966; Kahneman & Norman, can experience in a unit of time and the 1964) has suggested critical durations of 300 amount of information that can be processed msec, or longer for form perception. If from a single percept. Limits on the discrete luminance and contour information are rate of visual perceptions are set by the capa-summed over temporal intervals of this durability of the system for temporal resolution, tion, these summation intervals would set Bloch's law dealing with time-intensity reci-limits on the number of noninteracting per-iThis investigation was supported by United ce P ts that could be experienced in a unit of States Public Health Service Research Grant MH-time unless other mechanisms in the visual 1206 and a United States Public Health Service system served to terminate the integration Research Career Program Award K6-MH-22,014 esg with a ch j n stimu l a tion (Schur-2 Requests for reprints should be sent to Charles r _ .

Realizar un Trabajo Final de Maestría, no es fácil, menos en una situación de pandemia tan particular como la que surgió paralela al desarrollo de este trabajo. En un proceso que fue como una montaña rusa, con muchos altos, pero también muchos bajos; considero importante resaltar cada uno de los aportes realizados, así como los esfuerzos extra que implicaron para todos afrontar una situación desconocida, pero que finalmente me permitieron culminar la maestría con éxito.En primer lugar, agradezco a mi directora Natalia Villamizar, quien me ha guiado a través de cada una de las etapas de este largo proceso, con las condiciones particulares de la virtualidad para finalmente alcanzar los resultados satisfactorios que buscaba desde que decidí estudiar una maestría.

Forward and backward masking functions were obtained for both singleletter (SL) and twelve-letter (12-L) visual displays. A pattern mask with three energy levels, high (Ea), equal (Ez), and low (Ei), relative to the test field, was used. The Ei mask did not significantly mask the SL display at any stimulus onset asynchrony (SOA), nor when presented forward of, or simultaneous with, the 12-L display. However, Ei did mask the 12-L display when delayed, and was identical to the E a and E 3 masking functions at SOA ;> ISO msec. This result, in conjunction with greater backward than forward masking of the 12-L display for all masks, provided support for an interruption interpretation of backward masking for pattern mask delays of ISO msec, or greater.

Backward-masking functions for two schizophrenic groups were compared with the masking functions for two control groups (college students and nonschizophrenic psychiatric patients). Masking functions were obtained for both singleletter and eight-letter visual displays. The procedure involved a forced-choice letter recognition method analogous to signal detection methodology. Both schizophrenic groups produced longer masking functions, under all conditions, than the two control groups whose functions were highly similar. Consistent with "attention" theories of schizophrenia, results indicated that some deficit occurs in schizophrenia at a very early stage of information processing in the visual system.1 This paper is based on a doctoral dissertation by the first author under the direction of the second and third authors. The authors are indebted to the Veteran's Administration Hospital in Cleveland, Ohio, for allowing the use of its patients for subjects.2 Requests for reprints should be sent to Dennis

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