An isolation effect in serial memory for spatial information

This paper reports the first demonstration of an isolation effect or von Restorff effect (von Restorff, 1933 von Restorff, H. 1933. Uber die Wirkung von Bereichsbildungen im Spurenfeld [On the effect of spheres formations in the trace field]. Psychologische Forschung, 18: 299–342. [Crossref] , [Google Scholar]) in the context of a spatial-memory task: Short-term serial recall was enhanced for both the location and the serial position of one red dot presented amongst a sequence of otherwise black dots. When the serial position of the isolate was fixed, the spatial isolation effect only emerged when participants received a control block of trials before the block of isolation trials (Experiment 1). However, when the serial position of the isolate was varied across isolation trials, an isolation effect was still produced regardless of condition order (Experiment 2). It is suggested that both temporal grouping strategies and greater item-specific processing may have contributed to the enhanced retention of the isolate.     

Chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>) show the isolation effect during serial list recognition memory tests

The isolation effect (or von Restorff effect) occurs when one item in a to-be-remembered list is distinctive from all remaining items, and memory for that item is enhanced. Four chimpanzees were presented with a serial list of four photographs. In the homogeneous condition, all list items were from the same semantic category (e.g., four fruits). In the isolate condition, three items were from the same category, but the fourth item (the isolate) was from a different category (e.g., three fruits and one toy). Then, two photographs were presented, and the chimpanzees had to select the one that was from the list. Two of four chimpanzees were significantly more likely to select a correct isolate item than an item from the same list position in the homogeneous condition for at least some list positions. This facilitation in performance was for isolate items only, as presenting an isolate item in a list did not facilitate greater recognition of other list items compared to the homogeneous condition. These results indicated that some chimpanzees perceived the semantic categories of the photographs, and categorization of photographs led to the isolation effect. Thus, chimpanzees may share with humans some aspects of memory organization that involve spontaneously categorizing visual stimuli and recognizing categorically unique stimuli.     

An Exploratory Study of Discrimination of Composer Style

With an alternate study-test procedure, 254 college students attempted either to free-recall or rearrange in order items of an 11-CVC serial list to a criterion of two consecutive perfect trials. Ss learned the list with or without an isolate which was placed on each of the 11 serial positions. The main findings were as follows: (a) While the reconstruction condition required fewer study trials to criterion than the free-recall condition, the isolation effect occurred equally in both conditions. (b) The isolation effect was a function of the serial position; the effect was greater at the central positions than at the peripherals in free-recall and this trend was essentially reversed in the reconstruction condition. (c) In free-recall, no reliable and systematic spreading effect was obtained for the items immediately preceding and following the isolate; however, a positive spreading effect occurred concurrently with the isolation effect in the reconstruction condition. The isolation effect has been accounted for by a selective rehearsal assumption. Implications regarding the functional cues in serial order learning and the isolation effect in serial learning are suggested.     

Distance and ratio effects in the flanker task are due to different mechanisms

When participants must respond to a relevant central target and ignore irrelevant flanking stimuli the flanking stimuli produce a compatibility effect, with increased response speed and accuracy on compatible as compared to incompatible trials. This flanker effect is larger when compatible trials are more frequent than incompatible trials (the ratio effect). A potential explanation of this ratio effect is that the occurrence of frequent incompatible trials causes the focus of spatial attention to be set narrower than when there are frequent compatible trials. The present investigation tests this hypothesis by comparing the flanker effect with near and far flankers. The hypothesis predicts that the flanker distance should modulate the ratio effect more when incompatible trials are frequent than when compatible trials are frequent. The results, however, show the opposite pattern: Distance effects are larger in conditions with frequent compatible trials. Moreover, the effect of distance but not the ratio effect was eliminated when flanker distance remained fixed across blocks of trials, and also when participants had to attend to flanker stimuli in a go-no-go task. These results suggest that the ratio effect does not result from an adjustment of the focus of spatial attention.     

Long-term effects of testing on the recall of nontested materials

The isolation paradigm is a staple in the study of distinctiveness and memory. Isolated items are better remembered than non-isolated controls, and the standard interpretation of this effect is that subjective experience of salience recruits extraordinary processing to the isolated item. This interpretation is at odds with data showing an isolation effect when the isolate is not perceived as salient (e.g., von Restorff, 1933). All available research on the early isolation effect has tested memory after a relatively short retention interval. Perhaps the effect of salience on memory in the isolation paradigm would be revealed following longer retention intervals. The experiment reported here examines the effect of isolation following a 48-hour retention interval when the isolate evokes an experience of salience compared to when the isolate does not evoke that reaction. The isolation effect was substantial after the 48-hour delay but equally so for early and late isolation. Salience appears to have nothing to do with the memory processes even at the longer retention intervals.     

An adjacency effect in free recall

An adjacency effect was demonstrated at a high level of significance in the free recall, by 123 subjects, of a list of 40 high-frequency nouns presented in varying order on successive trials. The phenomenon referred to as the adjacency effect consists of the fact that when a subject is given repeated trials of study and free recall of a list of words (always presented in a different order), the probability of recalling a given item is greater when the item is presented temporally adjacent to an item which is already learned (as evidenced by recall on the previous trial) than when the item stands temporally between other items which are not yet learned. The enhancement of recall is greater when the item is presented between two previously learned items. The implications of the adjacency effect for verbal learning theory, particularly for the serial-position effect in serial learning and the concepts of interference and neural consolidation, are discussed.     

Temporal-spatial memory: retrieval of spatial information does not reduce recency

Factors influencing the shape of serial position curves in non-verbal serial short-term memory were examined, using a task testing memory for the position of dots. Similar recency slopes were found when both position and order were recalled (Experiment 1A) and when order only was required (Experiment 1B). This observation was confirmed and tested further in conditions requiring the same encoding but different amounts of spatial information at retrieval (Experiment 2). However, Experiment 2 also revealed an effect of spatial information retrieval on the overall level of memory for recency items. Overall, the results indicate that spatial items produce bow-shaped serial positions curves in tasks requiring the maintenance of order information and that recency is affected by the demand on spatial information retrieval in terms of the overall level of performance but not in terms of the recency slope. These findings are contrary to what is found in the literature on serial verbal recall when both item and order information are required.     

Initial codes for order in memory

The roles of positional and associative information in preserving the order of short sequences of items were investigated either by presenting an item in the same serial position on successive trials (position transfer), or by presenting the same pair of items in adjacent but shifted positions on successive trials (association transfer). While Experiment I found that positive transfer of position information occurred after just one repetition of an item in the same serial position, Experiment II found no evidence for association transfer after a single trial. If an item is presented in the same position, or if a pair of items are presented in adjacent positions on several successive trials, position transfer effects built up more rapidly than association transfer effects (Experiments III and IV). However, the rate at which association transfer effects are established depends on the type of item used, with lists of concrete words showing rapid establishment of associations (Experiment V) but lists of digits showing only slow development of associations (Experiment IV). It was concluded that serial order may be preserved both by positional and associative codes, but the establishment of an associative code is linked to the extraction of information about the items themselves.     

Serial position effects in recognition memory for odors: A reexamination

Seven experiments examined recognition memory for sequentially presented odors. Following Reed (2000), participants were presented with a sequence of odors and then required to identify an odor from the sequence in a test probe comprising 2 odors. The pattern of results obtained by Reed (2000, although statistically marginal) demonstrated enhanced recognition for odors presented at the start (primacy) and end (recency) of the sequence: a result that we failed to replicate in any of the experiments reported here. Experiments 1 and 3 were designed to replicate Reed (2000), employing five-item and seven-item sequences, respectively, and each demonstrated significant recency, with evidence of primacy in Experiment 3 only. Experiment 2 replicated Experiment 1, with reduced interstimulus intervals, and produced a null effect of serial position. The ease with which the odors could be verbally labeled was manipulated in Experiments 4 and 5. Nameable odors produced a null effect of serial position (Experiment 4), and hard-to-name odors produced a pronounced recency effect (Experiment 5); nevertheless, overall rates of recognition were remarkably similar for the two experiments at around 70%. Articulatory suppression reduced recognition accuracy (Experiment 6), but recency was again present in the absence of primacy. Odor recognition performance was immune to the effects of an interleaved odor (Experiment 7), and, again, both primacy and recency effects were absent. There was no evidence of olfactory fatigue: Recognition accuracy improved across trials (Experiment 1). It is argued that the results of the experiments reported here are generally consistent with that body of work employing hard-to-name visual stimuli, where recency is obtained in the absence of primacy when the retention interval is short.     

Disruption of memory for lip-read lists by irrelevant speech: Further support for the changing state hypothesis

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.     

Competition between a Simultaneous and a Serial Feature in Appetitive Feature positive and Feature negative Discriminations

Two experiments with rats examined competition between simultaneous and serial features for behavioural control in an appetitive discrimination. In Experiment 1, an auditory target was reinforced when presented in isolation. For different groups, the target was non-reinforced when simultaneously accompanied by a visual feature (first group), when preceded by a serial visual feature (second group), or when both accompanied by a simultaneous feature and preceded by a serial feature (third group). Tests performed after discrimination learning revealed inhibitory control by the simultaneous feature in the first group and by the serial feature in the second group. In the third group, the simultaneous feature acquired inhibitory control over the target in isolation, whereas the serial feature did not. However, the serial feature further reduced responding to the target-simultaneous feature compound relative to responding shown to the compound in isolation. In Experiment 2, the same training procedure was used in three groups as in Experiment 1, except that the target was nonreinforced in isolation and reinforced in the presence of a simultaneous and/or serial feature. Tests revealed that the feature acquired excitatory control in the first and second groups. In the third group, both features acquired excitatory control, although the control exerted by the simultaneous feature was less strong than that observed in the group trained with only the simultaneous feature. The theoretical implications of these results regarding competition between occasion setters and Pavlovian excitors and inhibitors were discussed.     

The role of timing deviations and target position uncertainty on temporal attending in a serial auditory pitch discrimination task

Listeners were presented with sequences of tones that ascended in semitone intervals. On each trial a single target tone in the sequence was displaced in pitch, and listeners were required to indicate whether the target tone was higher or lower than its normal pitch. Task constraints, specifically target serial position uncertainty and the probabilistic relationship between time deviations and target tones, were varied in order to determine the impact of task constraints on temporal attending strategy. When listeners had no advance knowledge of the serial position of the target, and early and late targets provided information regarding target serial position, performance was better for early and late target trials than for on-time target trials (Experiment 1). When listeners had no advance knowledge of the serial position of the target, and early and late temporal deviations provided no information regarding target serial position, performance for late target trials was superior to that for early and on-time target trials (Experiment 2). Finally, when target serial position uncertainty was eliminated, performance was equivalent across all three levels of target timing (early, on time, late). The results indicate that performance profiles based on stimulus timing properties are affected by various task constraints as well as by stimulus properties.     

Rats’ anticipation of current and future trial outcomes in the ordered RNR/RNN serial pattern task

In the ordered RNR/RNN serial pattern task, rats often reduce their running speeds on trial 2 less within the RNR than within the RNN series. Initially, investigators (Capaldi, 1985; Capaldi et al., 1983) considered this trial 2 differential speed effect evidence for rats’ anticipation of inter-trial outcomes within each series. Later findings, however, suggest that this effect reflects some generalization of the ordinal position of trial 3 (Burns et al., 1986) or its similar runway cues during trial 2 (Capaldi et al., 1999). To test these generalization hypotheses, we made trial 2 more distinct from trial 3 in each series by forcing rats to alternate runways in a T-maze only on the last trial rather than on trial 2 in each series in Experiment 1, or by forcing rats to alternate runways between trials rather than to run down the same runway on all trials within each series in Experiment 2. Although enhancing the distinctiveness between these trials reduced the trial 2 differential speed effect, extensive training failed to eliminate it. Therefore, this residual difference between trial 2 speeds could reflect rats’ anticipation of trial 3 outcomes during trial 2 as originally proposed by Capaldi (1985) Experiment 3 was designed to determine whether we could enhance rats’ final trial outcome expectancies during trial 2 by making different trial 2 choices distinctive cues for each trial 3 outcome. The trial 2 speed effect was greater when rats were forced to alternate over all trials only within one of the series than when they were sometimes forced to do so in either series. Post-training probe tests revealed that both series position and the relevant within-series runway events contributed to this enhanced anticipation of trial 3 outcomes.     

Multiple mechanisms for recency with vowels and consonants

Three experiments were conducted to test the hypothesis that the difference in recency effect between vowel-contrasting and stop-contrasting lists of syllables in immediate ordered recall can be explained by item discriminability and regular short-term memory mechanisms, without any recourse to echoic memory or precategorical acoustic storage (PAS). In Experiment 1, the short-term memory mechanisms were manipulated by reducing amount of output interference and length of retention interval. The partial-report technique was used. The most important finding was the usual final-position recency effect (difference in recall between the fifth and sixth serial positions) for the vowel lists but not for the stop lists, regardless of the type of report. Thus the PAS theory could not be rejected. In Experiments 2 and 3, the last item was differentiated from the other items of the list, either by lengthening the interstimulus interval between the last and the next-to-last (Experiment 2) or by increasing the intensity of the last item (Experiment 3). In both cases, an increase of the final-position recency effect was found even for stop lists. Since a drop in recall errors was also obtained for the fourth item when its intensity was increased (von Restorff effect), this final-position recency effect for stop lists is likely to be due to item discriminability, and not to echoic memory for the last item. Item discriminability appeared to be the critical factor.     

Serial position curves in spatial memory of rats: Primacy and recency effects

Memory for lists of items was tested in rats (N = 18) in an 8-arm radial maze. In Experiment 1 trials consisted of a study phase, in which the rat could freely choose five arms to obtain a food reward, and a test phase in which the animal was presented with a choice between a novel and a previously visited arm. The rat received additional food reinforcement only when visiting the novel arm. The two phases of a trial were separated by a retention interval of 30 sec or of 4, 16 or 60 min. It was found that recall of the five free arm choices was related to the serial position of the previously visited arm. There was a significant recency effect at the 30-sec delay. With longer retention intervals this disappeared, and a significant primacy effect could be observed. In Experiment 2 the same animals were given forced arm entries during the study phase and delays of 30 sec or 4 or 16 min before the test phase. Again, there was a trend towards a recency effect after the shorter delays and a significant primacy effect after the 16-min interval. These results show that, in the recall of lists of spatial items, rats have serial position curves with primacy and recency effects, depending on the length of the retention interval.     

Age-related differences in the von restorff isolation effect

When one item is made distinct from the other items in a list, memory for the distinctive item is improved, a finding known as the isolation or von Restorff effect (after von Restorff, 1933). Although demonstrated numerous times with younger adults and children, this effect has not been found with older adults (Cimbalo & Brink, 1982). In contrast to the earlier study, we obtained a significant von Restorff effect for both younger and older adults using a physical manipulation of font colour. The effect size for older adults was smaller than that obtained for younger adults, confirming a prediction of Naveh-Benjamin's (2000) associative deficit hypothesis, which attributes age-related differences in memory performance to older adults' reduced ability to form associations. The findings are consistent with related research in which older adults demonstrate similar—but smaller—benefits for distinctive information to those for younger adults.     

Focus identification during sentence comprehension: evidence from eye movements

Three eye movement experiments investigated focus identification during sentence comprehension. Participants read dative or double-object sentences (i.e., either the direct or indirect object occurred first), and a replacive continuation supplied a contrast that was congruous with either the direct or the indirect object. Experiments 1 and 2 manipulated focus by locating only adjacent to either the direct or indirect object of dative (Experiment 1) or double-object (Experiment 2) sentences. Reading-time effects indicated that the surface position of the focus particle influenced processing. In addition, Experiment 1 reading times were longer when the replacive was incongruous with the constituent that only adjoined, and particle position modulated a similar effect in Experiment 2. Experiment 3 showed that this effect was absent when only was omitted. We conclude that the surface position of a focus particle modulates focus identification during on-line sentence comprehension.     

Temporal isolation effects in recognition and serial recall

Recent temporal distinctiveness models of memory predict that temporally isolated items will be recalled better than temporally crowded items. The effect has been found in some tasks (free recall, memory for serial order when report order is unconstrained, running memory span) but not in others (forward serial recall). Such results suggest that the attentional weighting given to a temporal dimension in memory may vary with task demands. Here, we find robust temporal isolation effects in recognition memory (Experiment 1) and a smaller isolation effect in forward serial recall when an open pool of items is used (Experiment 2). Analysis of 26 temporal isolation effects suggests that the phenomenon occurs in a range of tasks but is larger when it is useful to attend to a temporal dimension in memory. The overall pattern of results is taken to favor memory models that rely on multiple weighted dimensions in memory, one of which is temporal.     

Does the isolation effect require attention?

An item that differs from the surrounding items is remembered better than an item that is consistent with its surroundings; this is known as the von Restorff effect or isolation effect (von Restorff, Psychologische Forschung, 18, 299–342, 1933). Theoretical explanations have proposed that the isolate is processed differently from control items, though some research has suggested that this processing might require more attention for semantic than for physical isolates. To test this possibility, in the present study we examined the isolation effects for physical isolates and semantic isolates under full and divided attention. Participants viewed lists of categorized words, with some lists containing either a physical or a semantic isolate, followed by immediate written free recall. Across three experiments, divided attention eliminated the semantic isolation effect but did not impact the physical isolation effect. Furthermore, semantic isolates were output earlier in recall than controls, whereas physical isolates were output more similarly to controls. These findings suggest that semantic isolation effects require attention during encoding, whereas physical isolation effects are relatively automatic.