Memory Scanning Task Research Articles

The manipulation of stimulus quality and the definition of stimulus encoding operations in memory scanning experiments.

Two experiments examine procedures for defining and isolating stimulus encoding processes within the standard memory scanning task. Two manipulations are used to converge on this definition: letter case (i.e., physical vs. name matching of letters) and stimulus quality. Experiment 1 produced equal scanning rates for the name match and the control conditions in which letter case was not varied. The physical match conditions produced scanning rates half as great as the control. None of these rates were greatly affected by the degradation (contrast reduction) of the probe stimulus, although the small difference in rates for the physical match condition was significant. Experiment 2 investigated two modes of stimulus degradation, contrast reduction and the addition of visual noise. All of the results of the first experiment were replicated for both modes of degradation, with the exception of the change in the scanning rates for the physical match condition. In addition, visual noise produced greater differences between positive and negative response times than did contrast reduction, which did not differ from the high contrast control condition. These results indicate that an abstract internal code is derived during the encoding of the probe stimulus from which the effects of stimulus quality have been removed. Thus, factors that interact with stimulus quality in memory scanning tasks can be assumed to have a locus within the encoding stage of processing.

Sensitivity of some human cognitive functions to effects of methamphetamine and secobarbital

Sternberg's memory scanning task, Buschke's selective reminding task, and a time production task were given to 18 male subjects after they had received 10 mg of methamphetamine, 100 mg of secobarbital and placebo on separate days. Time production and learning that involved storage and retrieval of information in long-term memory were most sensitive to drug effects. Other measures of learning and memory scanning performance were not affected by either drug.

Memory Impairment in Epileptic Patients: Selective Effects of Phenobarbital Concentration

Nineteen epileptic patients were tested first under medium (week 1) and then under high (week 2) therapeutic levels of phenobarbital. Relative to response times of 20 controls with equivalent practice but without medication, response times of patients in a short-term memory scanning task were strikingly slowed during week 2. However, increased phenobarbital did not slow responses in a task requiring access to information in long-term memory.

Task Difficulty as a Mediator of Subject Strategy in Memory Scanning

A number of previous studies have shown performance to be mutable in the Stemberg memory-scanning task. Our results suggest that the difficulty of the task, and particularly of the list materials employed, may underlie a number of findings at variance with a strict scanning interpretation. Experiment I found that probes of letter-sets that form words are responded to faster than those of nonwords, irrespective of the number of list items. Experiment II replicated these findings and extended the investigation to the influence of practice in this situation. We conclude that criterion changes in the response-decision process provide a straightforward model for reaction-time effects when experimental conditions are perceived as differentially difficult.

The effects of practice with one positive set in a memory scanning task can be completely transferred to a different positive set

Recognition tasks in which the items have been assigned to one and only to one response category throughout an experiment typically reveal that the functions relating reaction time and positive set size are negatively accelerated and have slopes which decrease significantly with practice. The present experiments were designed to determine whether this practice effect is specific to the individual items practiced or if it depends, at least partially, on relations built up among the positive set items. The results permit rejection of both alternatives. In the extreme case tested, it was found that, after prolonged practice with the same items composing nested positive sets, these items could be replaced with unpracticed ones without producingany significant change in the effect of set size, reaction times, or error levels. Absence of change in overall reaction times in combination with stability of slope values leads to the conclusion that not only do those practice effects which are related to the set-size effect transfer exceedingly well to unpracticed items, but practice effects on all other stages involved in item recognition also show almost total transfer to unpracticed items. It is concluded that, under the conditions of these experiments, the gain (through practice) in efficiency in processing the stimulus is independent of the stimulus.

Encoding processes in memory scanning tasks

Three experiments are presented that deal with the effect of stimulus probability on the encoding of both alphanumeric characters and nonsense figures. Experiment I replicated a previous finding of an interaction between stimulus probability and stimulus quality in a memory scanning task with numbers as stimuli. Experiments II and III investigated the same paradigm with unfamiliar visual forms as stimuli, and no interaction was found. Results were interpreted as showing that probability affects the encoding mechanism only when the encoding process results in a representation of the name of the stimulus. When stimulus materials are visual forms without names, probability does not appear to affect encoding processes.

Evoked potential correlates of visual item recognition during memory-scanning tasks

Visually evoked potentials elicited by tachistoscopically displayed alphabetic stimuli were recorded at vertex from six human subjects during a series of item recognition tasks. When presented with a test stimulus, the observer had to decide whether it had been memorized previously (i.e., whether it belonged to the positive as opposed to the negative set) and made a choice reaction time response accordingly. P300 amplitude was unequivocally greater following positive letter presentations than it was following negative letter presentations. This result is consistent with a “template-matching” model of P30O enhancement, but, more importantly, it extends the potential generality of this theory beyond the detection of simple sensory stimuli to complex cognitive tasks and stimulus events. The latency of the second positive peak remained essentially invariant across all positive set sizes, a fact which suggested that it reflected the minimum time required to register or encode the stimulus input. In contrast, P300 latency increased as positive set size was increased, i.e., as information processing took longer to complete.

Generative processes in character classification: Evidence for a probe encoding set

The role of rehearsal in a varied set memory scanning task was investigated by asking the subjects to rehearse subvocally the one to four target characters cyclically at a self-paced rate until the probe was presented. After making a manual positive or negative response to the probe, the subjects reported the last item rehearsed before the probe was presented. The results indicate that, when the last rehearsed item matched the probe, RTs were significantly faster than when it differed. Mean RTs over target set size were generally well fit by linearly increasing RT functions, with comparable slope values for negative responses and positive responses when the last rehearsal was the same as or different from the probe. The data suggest that rehearsal may reduce the duration of the probe encoding stage through some mechanism of pathway activation by providing the subject with a generated representation of what may appear next as a probe.

Effect of Association Value in a Memory Scan Task

The effects of association value of nonsense forms on reaction times of 16 college students on a Sternberg-type recognition-memory task were examined. Results indicated a linear relation between RT and length of the memorized list for high association-value forms but a non-linear relation for low association-value forms. These data support Briggs' (1974) conclusions regarding the nature of the RT/list length function.

The attentional demands of negation in a memory-scanning task

Subjects were run in a Sternberg recognition memory task modified to occasionally require a transformation prior to response. The transformation was similar to logical negation since onplus or nontransformed trials subjects responded "yes" if the probe was from the current memory set and "no" otherwise, while onminus or transformed trials subjects responded "no" to memory set probes and "yes" to nonmemory set probes. Two models proposed to account for the effects of logical negation were compared: The encoding and comparison model predicts that logical negation requires an additional processing stage, while the capacity sharing model argues that negation adds a processing stage and also retards the rate of memory search. The results indicated that minus probes had 50% larger mean reaction time by set size slopes than the corresponding plus probes. This finding offers clear support for the capacity sharing model.

Organizational properties in a cutaneous memory-scanning task.

An experiment investigated the notion that organizational properties operate in a memory-scanning task using cutaneous stimuli. The results indicated that the open-closed nature of the positive set is a significant factor in a cutaneous memory-scanning task. Set-size was not a significant factor. The data suggest there are some organizational processes in a cutaneous memory-scanning task, however, these processes do not seem to be completely analogous to those used in visual and auditory memory-scanning tasks.

Accuracy and speed strategies in scanning active memory

The effect of speed and accuracy payoff on performance in a short-term memory scanning task was investigated under two conditions of familiarity of material and two conditions of payoff. Memory sets and probes were either drawn from a small well learned pool of words (thefamiliar set) or were sampled without replacement from a very large pool of words (theinfinite set). Under both payoffs the infinite memory sets were searched at a faster rate than the familiar sets. The speed payoff reduced the constant component of latencies and, contrary to previous findings, increased the rate of memory search for both sets. Errors increased from about 1% with accuracy payoff to 19% with speed payoff. Under speed payoff most of the errors were false positives for the familiar set and false negatives for the infinite set. Several models of the task were considered, but none proved entirely satisfactory.

High-speed memory scan as a retention interval activity in short-term memory

A Sternberg high-speed memory scan task was used as a retention interval activity in a standard Brown-Peterson paradigm. Two levels of Sternberg search set, one or five items, were employed to see if the differential memory load produced by the different size search sets resulted in differential recall in the Brown-Peterson task. A comparison was made to a control condition in which S was required to shadow digits during the retention interval. No differential effect on recall of memory load was found when the Sternberg tasks were compared across three different retention intervals. Very little forgetting was produced by the Sternberg tasks as compared to the digit shadowing condition. Results are discussed in terms of the need for verbal activity to prevent rehearsal in short-term memory.

Incidental learning of words used in a memory scanning task

Incidental learning data was obtained by testing if Ss recognized words previously used in a memory scanning task. In the memory scanning task, Ss had compared probe words to memory sets consisting of one to four words, responding positively if the probes matched one of the memory set words or otherwise responding negatively. The incidental learning scores differentiated between certain memory set conditions: (1) Words from memory sets of one had higher scores than those from larger memory sets. (2) Positive probe words were better recognized than all other words. (3) There were no differences between memory sets larger than one item.

Specialization of the cerebral hemispheres in scanning for information in short-term memory

Lateral specialization of function in the cerebral hemispheres was investigated in the context of a memory scanning paradigm. The S first memorized a set of letters (the memory set) and then indicated whether or not a subsequent test stimulus, presented in either the right or left visual field, matched any letter in the set. The test stimulus was either a letter or a picture of some common object; for the picture, S’s response was based on the initial letter of the name of that object. Reaction time was recorded and plotted as a function of the number of letters in the memory set. The results support the hypothesis that in a memory scanning task of this type, letter and picture test stimuli are spatially and verbally represented, respectively, and are processed in different cerebral hemispheres.

Interhemispheric transfer of test stimulus representations in memory scanning

Test stimuli were presented in either the right or left visual field during a memory scanning task. The Ss indicated whether or not a given test stimulus, either a letter or a picture, matched one of a previously presented set of letters. Reaction times were recorded and plotted as a function of the size of the set of letters. The results are in agreement with the hypothesis that the two types of test stimuli are processed by different cerebral hemispheres with differing stimulus representations.

Effects of serial position and delay of probe in a memory scan task.

Effects of serial position and delay of probe in a memory scan task.