Stimulus factors and listening strategies in auditory memory: An experimental demonstration

Three experiments are reported in which digits spoken at different rates were recalled and monitored. In Experiment I, digits to be recalled were embedded in varying levels of noise. In Experiment II noise was presented only during the inter-digit intervals, either to the same or to the opposite ear as the digits. In Experiment III Ss monitored these sequences for a specified digit and reported its successor. Stimulus rate and signal-to-noise ratio affected perceptual processing time, as evidenced by the frequency and relative proportion of item and order errors. These stimulus factors induce listening strategies that influence the shape of the serial position curve and that persist after stimulus conditions are changed. The data are consistent with a two-stage processing model for the temporal course of speech perception and the nature of listening strategies.     

Stimulus factors and listening strategies in auditory memory: A theoretical analysis

A theory for the temporal course of perceptual coding during auditory short-term memory tasks is described. A low-level “sensor” and a high-level “identifier” process item and order information from stimulus word-strings. Both word durations and interword pauses are needed for this processing, and if adequate processing time is unavailable, perceptual delays will lead to degraded recall performance. Stimulus parameters and subject strategies interact to determine the quality and the order in which stimulus items are coded. These hypotheses are supported both by experiments using grammatical sentences and those using lists of unrelated words.     

Stimulus suffix effects in recognition memory

Recall of auditory items can be disrupted by presentation of an irrelevant auditory stimulus (a stimulus suffix). Previous researchers have suggested that suffix effects are not found on recognition tests. Two experiments are presented here that demonstrate suffix effects on recognition tests. These results suggest that suffixes interfere with item information and that suffix effects cannot be attributed solely to retrieval processes.     

Stimulus exposure time and perceptual memory

The recent explosion of research on implicit memory has facilitated the examination of perceptual and conceptual processes in the encoding of information. Nevertheless, stimulus exposure time—the amount of time that a stimulus is physically available to a perceiver’s scrutiny—has received little attention. In the present paper, we examine the effect of stimulus exposure time on three implicit memory measures (word-fragment completion, perceptual identification, and general knowledge) and two explicit memory measures (graphemic cued recall and semantic cued recall). In Experiment 1, we demonstrated that increases in exposure time lead to increases in implicit perceptual memory, but not to implicit conceptual memory, when the encoding task focuses on perceptual features of the stimulus. We replicated this effect in Experiment 2 and demonstrated that increases in exposure time lead to increases in perceptualand conceptual memory when the measures are explicit. Thus, the current experiments demonstrate that manipulations of exposure time lead to dissociations in implicit, but not explicit, memory.     

Stimulus comparison strategies and task demands in successive discrimination

This research isolates two distinct strategies used to identify stimuli presented at different rates in successive discrimination tasks. The short-term strategy (used at rapid rates) compares current stimuli to immediately prior stimuli present in sensory or other short-term storage, whereas the long-term strategy (used at slow rates) compares current stimuli to a standard stimulus in long-term memory. In Experiment 1, subjects detected a medium-duration tone amid both long and short distractors. Analysis of false alarms indicated that strategy choice is strongly influenced by event rate, and therefore by the presence or absence of sensory traces of preceding stimuli. Experiment 2 was designed to force subjects to use the short-term strategy (to detect targets, present stimuli had to be compared to their immediate predecessors), and varied the event rate. Subjects were able to maintain a high level of performance throughout the task only at the fastest event rate. This pattern of results suggested that when the task demanded it, subjects could use a particular strategy, but if the event rate (and consequently the availability or otherwise of relevant memorial traces) was not favourable to that strategy, then performance was disadvantaged.     

Stimulus information and stimulus interference in bisensory short-term memory

An attempt was made to determine if Ss’ strategy of retaining stimulus material changed under conditions of bisensory simultaneous stimulation when one of the two inputs was relevant information as opposed to interference. Thus in Group 1 Ss were stimulated bisensorily, attended to both inputs (information), but recalled only one input. Ss in Group 2 were stimulated bisensorily, attended to only one input, and recalled only that input (interference). It was found that S’s efficiency of recall was decreased in the information condition (Group 1) but strategy was not altered. In both groups, Ss performed similarly; performance was in turn similar to that observed in the typical bisensory situation, i.e., where both channels are recalled.     

Stimulus similarity decrements in children's working memory span

Two experiments investigated the impact of the relationship between processing and storage stimuli on the working memory span task performance of children aged 7 and 9 years of age. In Experiment 1, two types of span task were administered (sentence span and operation span), and participants were required to recall either the products of the processing task (sentence-final word, arithmetic total) or a word or digit unrelated to the processing task. Experiment 2 contrasted sentence span and operation span combined with storage of either words or digits, in tasks in which the item to be remembered was not a direct product of the processing task in either condition. In both experiments, memory span was significantly greater when the items to be recalled belonged to a different stimulus category from the material that was processed, so that in sentence span tasks, number recall was superior to word recall, and in operation span tasks, word recall was superior to number recall. Explanations of these findings in terms of similarity-based interference and response competition in working memory are discussed.     

Stimulus selection and the number of stimulus components

The number of word components in the compound stimuli of paired-associate lists were varied, and the words within a compound were presented either in a constant or in a variable order from trial to trial. The number of components, above one, had no appreciable effect on the difficulty of learning, and the variable order lists were more difficult than the constant order. Recall with the word components as cues showed that the amount of selection decreased with the variable order lists as the number of components increased. With the constant order lists, selection tended to remain constant as number of components increased. This was interpreted as the result of the availability of a rule for selection in the constant order conditions.     

Stimulus control of information processing in pigeon short-term memory

Six pigeons were trained initially on a delayed successive matching-to-sample task using red and green fields as sample and test stimuli. Following acquisition, each sample was followed either by a vertical line (“remember” cue), which indicated that sample memory would be tested, or by a horizontal line (“forget” cue), which indicated that sample memory would not be tested. During the experiments, sample memory on forget trials was tested occasionally. A series of five experiments revealed: (a) better retention on remember trials than on forget trials, (b) increased effectiveness of a forget cue when it followed closely sample offset, (c) more rapid forgetting over a retention interval ranging from 3 to 6 sec on forget trials than on remember trials, (d) a “cancellation” effect in which a remember cue which followed immediately the offset of a forget cue attenuated markedly the effectiveness of the forget cue, and (e) an “insulation” effect in which the effectiveness of a forget cue was reduced considerably when presented after a remember cue. It was concluded that pigeons actively process or rehearse the sample memory during the retention interval.     

Stimulus array and recall method as variables in audio-visual split-span memory

Performance on an audio-visual split-span task was found to be adversely affected by the concurrent operation of two factors, namely: alternation of stimulus classes between the two input messages, and the use of a recall method which entails alternate sampling of the two messages. However, these factors had no significant effect when operating singly. The present study indicated that subjects prefer the strategy of reporting visual items first when using modality recall, and that this strategy is more efficient than that of reporting auditory items first. Also, modality recall proved to be the preferred method under free recall instructions. While there were more visual errors than auditory errors, visual commissions exceeded order errors, but auditory order errors exceeded commissions. The redundancy proposal of the search hypothesis (Yntema and Trask, 1963) was tested, and was found to be inadequate as an account of audio-visual performance.     

Stimulus selection with duration as a relevant cue

To date, research has not explicitly examined how duration competes with other stimulus dimensions for control over responding. The present study investigated some familiar selective mechanisms of stimulus control over key pecking in pigeons, with duration and line tilt as discriminative stimuli in successive discrimination procedures. Specifically, pigeon's key pecking was reinforced with food or extinguished following compound stimuli comprising one of two line orientation stimuli presented for one of two different durations. Traditional experimental designs explored stimulus additivity, overshadowing, blocking, and learned irrelevance. Although stimulus additivity was observed, control by duration was masked by line tilt in extinction testing that followed facilitated acquisition with redundant, relevant cues. In addition, although prior training with duration relevant partially blocked subsequent acquisition of control by line tilt when both stimulus dimensions were relevant, there was a tendency for control by duration to decrease with continued compound training. It was suggested that the greater time required to distinguish duration on a trial—compared to more commonly studied stimulus dimensions, which can be distinguished almost immediately—puts duration at a competitive disadvantage in situations where other relevant dimensions are also available.     

Working memory and strategies in syllogistic-reasoning tasks

It has often been asserted that working-memory limitations are a major factor contributing to problem difficulty; for example, Johnson-Laird’s (1983) mental-models theory appeals to working memory limitations to explain the difficulty of syllogistic reasoning. However, few studies have directly explored working memory in problem solving in general or syllogistic reasoning in particular. This paper reports two studies. In the first, working-memory load was varied by presenting syllogistic tasks either verbally or visually (so that the premises were continuous1y avai1ab1e for inspection). A significant effect of memory load was obtained. In the second study, premises were presented visually for a subject-determined time. Dual-task methods were used to assess the role of working-memory components, as identified in Baddeley’s (1986) model. Syllogistic performance was disrupted by concurrent random-number generation but not by concurrent articulatory suppression or by concurrent tapping in a preset pattern. Furthermore, the concurrent syllogism task interfered with random generation and to a lesser extent with articulatory suppression, but not with tapping. We conclude that while the central-executive component of working memory played a major role in the syllogistic-task performance reported here, the articulatory loop had a lesser role, and the visuospatial scratch pad was not involved.     

Stimulus array onset as a preparatory signal in attentional selection

Warning signals enhance psychomotor performance by optimising preparation for the arrival of an event. Recent evidence, however, suggests that a warning signal can also disrupt attentional preparation by interfering with the process of preparing. It was hypothesised that a warning signal consisting of a change to the task-relevant items (array onset) may be more effective than a traditional warning signal consisting of the arrival, or removal, of a bar-cue which is independent of the task array. In three experiments array onset was a more effective warning signal than the bar-cue because reaction times were significantly faster without an increase in errors. In addition, an auditory warning signal resulted in faster reaction time than the bar-cue but in performance equivalent to that with an onset warning signal. Thus, the superiority of an auditory warning signal, reported by Davis and Green, was not found, when the interference of the visual warning signal with preparation was reduced. These results suggest that a visual warning signal consisting of a change to the stimulus array is more effective than an event independent from the stimulus array.     

Stimulus generalization along a dimension based on a verbal concept

The present study examined generalization along a dimension based on a verbal concept of occupational status. The status dimension was scaled by students who placed occupation names into five status categories, Category 1 representing highest status and Category 5 the lowest status. In two experiments, key presses by students were occasionally reinforced when a slide showing an occupation name from Status Category 3 was present. For half the subjects, key presses were not reinforced during a name from Category 1; for the other half, presses were not reinforced during a name from Category 5. Occupation names from all status categories were later singly presented. In this generalization test, subjects typically divided the dimension into two parts, responding alike to all names within each part. The results suggest that generalization along a dimension in humans is mediated by a subject's verbal classifications of stimuli.     

A model of memory in concept learning

A concept learning model was developed and tested in two conjunctive attribute identification tasks. The model includes assumptions about the focus of attention, decision making, and memory for stimulus information and prior decisions. Predictions are made about how S changes his hypothesis following an error. Procedures in both tasks allowed inference of the subject's current hypothesis. The hypothesis selections and error statistics were in the majority of cases accurately predicted by the model. Deviations from predictions on hypothesis sampling occurred for naive Ss but not for trained Ss who were required to state a hypothesis on each trial.