We measured latency and speed of verbal responses to letters presented simultaneously (Experiment I) or in succession (Experiment IT). In simultaneous presentation and within the limits of memory span, response latency increases proportionally to the number of. responses. In successive presentation, the same function is found when more than three responses are given. In both situations, response speed is constant. The increase in latency is about 70 msec per response. Such a duration is too long to be explained by a process of encoding but too short to result from subvocal rehearsal. This latency seems to correspond to the preparation of the response.The span of immediate memory has been investigated by many authors, but little attention has been given to variations of latency as a function of the number of items recalled.The hypothesis tested here is that latency of the first response will increase with the number of items recalled. The aim of the present study is to examine the factors associated with this increase in latency. Is this increase due to processes of reception and processing of information or is it due to the preparation of the response?In order to test the value of these two explanations, two situations which are classical in the study of immediate memory were compared. In one situation (Experiment I), stimuli were simultaneous and brief; in the second (Experiment II), they were presented successively. In both situations, the same type of response was required from the subject. The comparison of these two situations should enable us to clarify the respective role of the input and the output.Furthermore, we measured the rate of responses, predicting that this index would throw some light on how information is processed.
EXPERIMENT I
Response Latency to Letters Presented SimultaneouslyWe measured the latency of the first response to a brief presentation of one to five letters.Materials. The material consisted of the letters of the alphabet, with the exception of G, I, N, P, Q and W, which were omitted to avoid visual confusion. random order on a circular surface (diameter, 28 mm; visual angle, 1.3 deg) and the subjects were asked to recall the letters without regard to order. Situation Bserial recall: The letters were arranged on a horizontal line, the space between two consecutive letters being 3 mm. Subjects were asked to recall the letters in order, from left to right.The number of letters printed on each card varied from one to five. For each number of letters and for each of Situations A and B, six different cards were constructed by randomly assigning letters to each card, so that an equally frequent presentation of all letters was obtained.
MethodProcedure. The cards were presented through a three-channel tachistoscope (Scientific Prototype, Model GB) during 50 msec, a duration that Sperling '(1967) judged sufficient for identifying five letters. Luminance was 10 fl.Before presenting the experimental material to the subject, the experimenter explained the two possible spatial arrangements an...