Repetition effects and signal classification strategies in serial choice-response tasks.
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Two experiments are reported in which age differences in working memory performance are explored. In the first study, young and older adults held 2, 3, 4, or 5 unrelated words in mind while verifying a single or complex sentence. An age-related decrement was found in subsequent serial recall of the words, and this decrement was larger with longer word lists. Experiment 2 confirmed the interaction between age and list length, using list lengths of 4, 6, and 8 words and a free-recall procedure. There was no interaction between age and divided attention in either experiment. Surprisingly, sentence complexity had a greater detrimental effect on recall in the younger group. The results are discussed in terms of articulatory rehearsal being augmented by using secondary memory in the case of younger subjects.
Encoding seen movement of another human body requires visuo-spatial processing, and recall involves motor activity. However, encoding whole body movement patterns is affected differently by patterned and spatial secondary tasks, and this difference is reversed for encoding of spatial targets for movement (Smyth, Pearson, & Pendleton, 1988). The experiments reported here investigate the rehearsal of such movement patterns and their recall over unfilled and filled intervals. Performing, watching, or encoding a sequence of spatial positions while carrying a memory load of movement patterns did not affect recall of those movements, whereas performing, watching, or encoding a further set of patterned movements reduced the number recalled from the original set. However, memory for a series of locations in space was not affected by watching patterned movements during the interval, and only order information was affected by watching movement to a series of spatial locations during the interval. The results are discussed in terms of the independence of rehearsal mechanisms for spatial sequencing and movement patterns.
In choice serial reaction time (RT), Response-to-next-Stimulus Interval (RSI) was varied from 0 to 600 msec in 40-msec steps. In three experiments, RT fell and errors rose as RSI was increased to 480 msec; they remained unchanged thereafter. The effect of RSI on RT was not linear, was reduced by 6- as compared with 4- or 3-choice responding, and was unaffected by sleep deprivation, despite loss of sleep reducing RT overall. The effect of penultimate RSI on RT was similar to that current RSI, but smaller. Two explanations of RSI--response-generated kinaesthetic feedback blocking a "central processor" and a preparatory interval as in warned simple RT--are rejected. Instead, the idea of "relative refractory state" is revived but now, because of the RSI/error finding, biased more towards responding than stimulus reception and encoding. In all three experiments the influence of RSI on RT was reduced with practice. If practice encourages automatic rather than controlled processing (Shiffrin & Schneider, 1977), the prediction is that the former will show less refractoriness.
This study examined different explanations of age-related impairments in recall of details from text and autobiographical events. An interpretation of Central Executive Capacity Deficit was supported and explored further. This suggests that details are more demanding of capacity than main points, and that ability to appropriately integrate details with context is likely to be impaired. An implication was that irrelevant and false information may occur, and this was supported in both autobiographical and text recall. The effects were then examined in relation to various measures of ability. The aim was to determine whether declining capacity (as indicated by "Fluid Intelligence" measures) predicted ability to recall in a detailed manner. The difficulty with details was predicted independently by chronological age and by measures of fluid (e.g. AH4 intelligence test) and the more crystallized verbal ability (Mill Hill vocabulary test). Only a measure of the specificity of autobiographical recall was predicted solely by measures of fluid intelligence. Decreased specificity was not a result of faster decay of memory for details, as there was little difference across the lifespan. The resource deficit appears to affect retrieval and appropriate implementation of detail. It was concluded that lower-ability elderly subjects have decreased Central Executive resources, which leads to poor (often inappropriate) integration of details with central thematic points, but that subjects' verbal ability, which does not decline with age, still has an important part to play.
Memory for visually presented items is impaired by speech that is played as an irrelevant background. The paper presents the view that changing state of the auditory material is an important prerequisite for this disruption. Four experiments studied the effects of sounds varying in complexity in an attempt to establish which features of changing state in the auditory signal lead to diminished recall. Simple unvarying or repetitive speech sounds were not sufficient to induce the irrelevant speech effect (Experiment 1): in addition, simple analogues of speech, possessing regular or irregular envelopes and using a range of carriers, failed to imitate the action of speech (Experiment 2). Variability of between-utterance phonology in the irrelevant stream (Experiment 3) emerged as a crucial factor. Moreover, predictability of the syllable sequence did not reduce the degree of disruption (Experiment 4) suggesting that supra-syllabic characteristics of the speech are of little importance. The results broadly support the idea that disruption of short-term memory only occurs when the speech stream changes in state. It is argued that disruption occurs in memory when cues to serial order based on phonological representations of heard material interfere with the phonological codes of visual origin. It is suggested that cues to changing state of the speech input contaminate those associated with items of visual origin, which are already in a phonological store.
Six experiments investigated the locus of the recency effect in immediate serial recall. Previous research has shown much larger recency for speech as compared to non-speech sounds. We compared two hypotheses: (1) speech sounds are processed differently from non-speech sounds (e.g. Liberman & Mattingly, 1985); and (2) speech sounds are more familiar and more discriminable than non-speech sounds (e.g. Nairne, 1988, 1990). In Experiments 1 and 2 we determined that merely varying the label given to the sets of stimuli (speech or non-speech) had no effect on recency or overall recall. We varied the familiarity of the stimuli by using highly trained musicians as subjects (Experiments 3 and 4) and by instructing subjects to attend to an unpracticed dimension of speech (Experiment 6). Discriminability was manipulated by varying the acoustic complexity of the stimuli (Experiments 3, 5, and 6) or the pitch distance between the stimuli (Experiment 4). Although manipulations of discriminability and familiarity affected overall level of recall greatly, in no case did discriminability or familiarity alone significantly enhance recency. What seems to make a difference in the occurrence of convincing recency is whether the items being remembered are undegraded speech sounds.
In studies of verbal short-term memory it has been shown that the length of words to be remembered affects the size of memory span. This word-length effect is attributed to relationships between the rate of rehearsal of verbal material and the time it takes to speak the words being rehearsed. For spatial memory span there may also be an internal rehearsal system linked to overt responding, and if there is a strong analogy to be drawn between the verbal and spatial domains then movement time between spatial targets should predict the number of spatial locations that can be recalled. In the experiments reported here the time taken to move between spatial targets is varied by altering the size of targets and the distance between them. No difference between span performance on a nine-block spatial span task were found, either on immediate recall or on recall after an interval. When recall is of items from an array of 27, grouped in nine sets of three, with only one location in any set being presented on any trial, there is an effect of display size. This effect is consonant with the argument that movement time is related to spatial rehearsal, but other explanations are also possible. However, if recall in this task is scored over the nine sets rather than over the 27 items, then there is no difference between the displays. The results indicate that performance on the normal nine-block spatial-span task cannot be predicted by movement time.
Two experiments critically re-examine the finding of Campbell and Dodd (1984, Experiment 2), which suggests that irrelevant speech disrupts the encoding of visual material for serial recall. Support is sought for the competing view that the effect of irrelevant speech is on storage by comparing the effect of a range of acoustic conditions on memory for graphic and lip-read lists. Initially, serial short-term recall of visually presented lists was examined with irrelevant speech that was both asynchronous with the visually presented items and of varied speech content (Experiment 1a). In this experiment substantial impairments in recall of both graphic and lip-read lists were found. However, with unvarying asynchronous speech (Experiment 1b) the effect of speech was small and non-significant. Experiment 2 examined the effect of changing state and of synchrony of speech with lip movements. When conditions of synchronous and asynchronous unvarying speech were contrasted, no significant effect of synchrony or irrelevant speech was found (Experiment 2a and 2c). In contrast, when the speech was varying in content, a strong effect of irrelevant speech was found; moreover, the effect was roughly the same for synchronous and asynchronous materials (Experiment 2b). The contrast in outcome with varying and unvarying speech provides strong support for the "changing state" model of the irrelevant speech effect. Coupled with the absence of an effect of synchrony in Experiment 2, these experiments reinforce the view that disruption by irrelevant speech occurs in memory, not at encoding.
Dual-task research has revealed a response-selection bottleneck: response selection cannot occur simultaneously in two different tasks, though perceptual processing may overlap response selection (Welford, 1952; Pashler & Johnston, 1989). In serial performance with preview, the same task is performed repeatedly, but stimuli are available well before response. Does the dual-task bottleneck limit the rate of responding in this situation, despite the fact that task set need not change? Four experiments examined manual responses to letters, varying stimulus preview. Preview increased RTs for the first response and reduce the subsequent inter-response intervals (IRIs). Preview also reduced the effect of visual intensity and response duration on IRIs, whereas effects of stimulus-response mapping variables were unchanged. These results indicate that the response-selection bottleneck limits serial performance, just as it limits concurrent performance of two unrelated tasks. This implies that the response-selection bottleneck is not caused by the need to switch task set.