Echoic memory processes in good and poor readers.

Four experiments were conducted to determine whether echoic memory plays a role in differences between good and poor readers. The first two experiments used a suffix procedure in which the subject is read a list of digits with either a tone control or the word go appended to the list. For lists that exceeded the length of the subjects memory span by one digit (i.e., that avoided ceiling effects), the poor readers showed a larger decrement in the suffix condition than did the good readers. The third experiment was directed at the question of whether the duration of echoic memory is different for good and poor readers. Children shadowed words presented to one ear at a rate determined to give 75-85% shadowing accuracy. The items presented to the nonattended ear were words and an occasional digit. At various intervals after the presentation of the digit, a light signaled that the subject was to cease shadowing and attempt to recall any digit that had occurred in the nonattended ear recently. Whereas good and poor readers recalled the digit equally if tested immediately after presentation, the poor readers showed a faster decline in recall of the digit as retention interval increased. A fourth experiment was conducted to determine whether the differences in echoic memory were specific to speech stimuli or occurred at a more basic level of aural persistence. Bursts of white noise were separated by 9-400 ms of silence and the subject was to say whether there were one or two sounds presented. There were no differences in detectability functions for good and poor readers.

Effects of stimulus probability on encoding by mentally retarded and nonretarded persons.

A choice reaction-time experiment was performed in which probe stimulus probability and probe stimulus quality were orthogonally manipulated. Subjects were retarded and nonretarded junior high school students. The stimuli were random forms presented at four probability levels in order to assess the effect of stimulus probability on the encoding process. The results indicated that the retarded subjects appeared to be less sensitive than did the nonretarded subjects to stimulus-probability information, particularly under degraded stimulus conditions. The results were discussed in terms of the relative sensitivity of retarded and nonretarded persons to stimulus-probability information and the effect of such information on the encoding process.