Short Time Recall As A Function Of Type Of Stimulus And Length Of Delay Interval Essay, Research Paper
Abstract
We were interested in examining patterns of short-term information recall. We used the Brown-Peterson distractor technique to investigate the effects of stimuli type and delay interval on recall for 17 Ss. Each S was tested under 4 conditions, combined of word triads or nonsense syllables triads, with a short (10-sec) or long (45-Sec) delay interval. S read aloud the visually presented stimulus items, and aurally recalled them after the delay interval, in which S was engaged in counting backwards in threes from a presented 3-digit number. Measures were taken only for recall proportion. Results suggest a significant difference in recall between words and nonsense syllables, with words significantly better recalled. For the delay interval, results show no significant effect, and thus differ from those obtained in previous research. This discrepancy is discussed in terms of technical differences in procedure. No other effect or interaction approached significance.
Short-term Recall As a function of
Type of Stimulus and Length of Delay Interval
Short-term memory (STM) has been vastly studied and tested. One of the popular testing methods for STM has been the short-term recall, in which S is shortly presented with a single or multiple items, later to be recalled. Various researchers have focused their studies on different aspects, while attempting to identify those factors that most strongly influence short-term recall. A short-term memory model based upon a limited capacity to process information suggests that the recall of verbal material can be effected by the activity which consumes the retention interval, referred to as the interpolated activity.
Diverse studies examine the significance of elements involved in the interpolated task. In general, researchers have attempted to prevent Ss from rehearsing, i.e., processing exposed stimuli by keeping the material within the short-term store through the use of rehearsal-preventing interpolated tasks. The most famous of these has been suggested in the Brown-Peterson technique (Peterson & Peterson, 1959) in the form of backwards counting. In the original Peterson studies (1959), Ss attempted to retain aurally presented consonants trigrams while counting backwards by three or four from a three-digit number. This interpolated activity was continued for some predetermined retention interval, immediately after which Ss were asked to recall the originally presented consonants. Using this technique, the Petersons demonstrated a very rapid decline in recall. The probability of recall decreased exponentially with duration of interpolated activity.
Murdock (1960) investigated the effect of the stimulus type and the effect of varying the rate of interpolated activity. Similarly to the Petersons (1959) he found that in all cases forgetting, whether measured by accuracy or latency, increased with the duration of the interpolated activity. In addition, Murdock suggested little difference between the retention of three consonants and three words; consonant syllables and word triads were equally well recalled.
Murdock (Tell, 1971) has shown that short-term recall is effected by whether the presentation is visual or auditory. According to Neisser (Tell, 1971) there is an auditory-storage system which results from auditory input and can function as a source of information in short-term recall. This temporary storage system is referred to as echoic memory. ?Echoic memory is passive, continuous, composed of sounds, and decays rapidly? (Tell, p. 150).
However, auditory input may also function as auditory noise. Voiced recall, vocalized irrelevant interpolated activity, or certain types of presentation conditions can mask, erase, or overwrite information available in the echoic memory store. This assumption is especially important when considering the interpolated activity. Tell (1971) suggested that a verbal interpolated task, in addition to its role as a rehearsal-prevention activity, would also produce auditory feedback, which masks information from echoic memory.
Tell and Ferguson (1974) further explored this issue of vocalization by examining the influences of active and passive vocalization on short-term recall. As distinguished by Crowder (Tell & Ferguson, 1974), active vocalization refers to presentation conditions where the to-be-remembered stimulus items are voiced aloud by S as they are visually presented. Under passive vocalization conditions, S listens to E read each stimulus item as it is visually presented. Tell & Ferguson suggested that active and passive vocalization differ mainly at the longer retention intervals, with recall much higher under the passive vocalization condition. This supported the idea that active vocalization could interfere with effective rehearsal or encoding strategies.
Another variable manipulated in search of significant effect on recall is whether interpolated tasks were rewarded or not. Soucar, Walk, and Covert (1971) suggested that retention of syllables is reduced under rewarded conditions. However, productivity and accuracy of the actual interpolated tasks was unchanged by reward.
The present experiment is designed to examine short-term recall as a function of stimulus type and length of delay interval. We hypothesize that both variables will be found to be significant. Specifically, we predict that: 1) recall proportion will be higher for words in compare to nonsense syllables; 2) recall proportion will decrease with the increase of delay intervals.
Method
Participants
Seventeen Hunter undergraduate psychology students served as Ss; twelve were female. Their age range was 18-32. They were demanded to participate in the experiment as part of their Experimental Psychology course requirement.
Apparatus The group of participants was assigned to pairs, who conducted the experiment in small cubicles, so that each pair worked independently of the other pairs. However, cubicles were not soundproof. Each of the participants served both as S and as E, in alternation with his/her partner. Two sets of stimuli were presented: nonsense syllables and words. The class of participants constructed both sets of stimuli. Each E individually selected twenty-four nonsense syllables and another twenty-four words out of two separated class-constructed lists. A nonsense syllable was defined as a vowel surrounded by two consonants, and was selected in such a way as to minimize association value and avoid acronyms or similarity to any other selected syllables. The words were 3-5 letters long, mostly nouns, and withdrawn from different categories.
The stimuli were presented on white index cards; each 12.5 X 7.5 cm in size. Each set of stimuli (words or nonsense syllables) constituted of eight cards. Each stimulus card had either three nonsense syllables or three words hand written by pen (black or blue), and located at the center of the card. Size of letters was not precisely controlled, but was considered appropriate if enabled the S to see it from about two feet away from card. On the opposite side of the stimulus card was a randomly selected three-digit number, similarly written and located. Either standard hand watches or digital stopwatches measured 45 or 10-sec delay intervals.
Procedure
All sixteen subjects received a 16-trial sequence, involving the presentation of 16 word or nonsense syllables triads. Each trial consisted of a short visual presentation of the stimuli, manually performed by E, who set opposite to S. The active vocalization condition required Ss to read the triads aloud while they were shown. Using the Brown-Peterson distracter technique (Peterson & Peterson, 1959), Ss attempted to retain item triads while performing an interpolated task. The interpolated task involved counting backwards in threes from a presented three-digit numeral. Two lengths of interval delays were used: 10 or 45 sec. Once the interval delay was over, S would immediately stop interpolated activity, and orally recall each item, regardless of its order of position within the triad. E recorded retention scores, which ranged from 0 to 3, with 1 point given for each correctly recalled item. Performance on the interpolated activity was not recorded. Order of stimuli presentations were constructed in such a way that no type of stimulus followed itself. Stimuli were presented in the following order: 1) four words-short interval; 2) four nonsense syllables ? long delay; 3) four words ? long delay; 4) four nonsense syllables ? short delay.
Results
The data of each S were scored in terms of the correct number of items recalled, regardless of the items? positions within the triad. An overall analysis of variance was performed on the recall scores. Since one group of Ss was tested under the entire four conditions (repeated measures), a within-subjects ANOVA was computed for a two-factor design. Stimuli type served as factor A, while delay interval served as factor B. The only significant effect found was the type of stimulus presented. As seen in figure 1, recall was significantly better for words than for nonsense syllables under both retention intervals {F (1,16)=30.96, P* .05}. Tests of simple main effects for type of stimuli again showed recall of words (9.3) superior to nonsense syllables (7.02). No significant difference was found in main effects for length of retention interval; recall did not decline with the increase in delay interval {F (1,16)=0.005, P* .05}. No significant interaction (one that would indicate differences not explainable by main effects) was found between factors A & B, i.e., between stimulus type and retention interval {F (1,16)=0.76, P*.05}. In summary, only type of stimuli was found to have a significant effect on recall performance, with a superiority of words over nonsense syllables.
Discussion
The above-described results lend support to our hypothesis that words are better recalled than nonsense syllables. As predicted, this effect of type of stimuli was found to be significant. However, for the effect of length of delay interval, our results significantly differ from those obtained by previous studies. Peterson & Peterson (1959), Murdock (1960), and Tell (1971) have all shown a decrease in the proportion of recalled items as a function of increased retention intervals. In all of these cases, forgetting increased with the duration of the interpolated activity. Our results suggested no significance to the delay interval effect. This discrepancy might be explained in terms of technical differences in procedures.
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