Auditory and visual serial position functions obey different laws

Rhesus monkeys were tested in serial probe recognition tasks with either travel slide pictures or natural sounds. Tests with four-item lists produced serial position functions that were essentially opposite in shape for the two modalities and changed in opposite ways with retention interval. For visual memory, the primacy effect grew and the recency effect dissipated with retention interval. Capuchin monkeys, humans, and pigeons showed similar results. For auditory memory with rhesus monkeys, the recency effect grew and the primacy effect dissipated with retention interval. These results taken together, along with results from rehearsal tests of monkeys and humans, implicate two passive memory processes with different time courses. Interference among items within auditory lists was manipulated by varying the time between items and categories of items. Interference across lists was manipulated by varying the item pool size and, hence, item repetitions. Changes in the auditory serial position functions indicated that proactive and retroactive interference may have been instrumental in these dynamically changing serial position functions. Implications for theories and models of memory are discussed.     

Auditory List Memory in Rhesus Monkeys

Auditory memory of 2 rhesus monkeys was tested in a serial probe recognition task. Lists of four environmental or natural sounds were followed by a retention interval and a test. The test matched one of the list items on half of the trials. The retention interval was varied across sessions. Six experiments showed similar results and changes in the serial position function. At short retention intervals, there was good memory for first list items (primacy effect) and poor memory for last list items. At intermediate retention intervals, memory improved for last list items (recency effect). At long retention intervals (20 s and 30 s), the recency effect was strong, and the primacy effect had dissipated. These auditory primacy and recency effects and their changes with retention interval were opposite to those for visual memory. Implications for processes and mechanisms of memory are discussed.     

Monkey memory: same/different concept learning, serial probe acquisition, and probe delay effects

Three rhesus monkeys were trained and tested in a same/different task with six successive sets of 70 item pairs to an 88% accuracy on each set. Their poor initial transfer performance (55% correct) with novel stimuli improved dramatically to 85% correct following daily item changes in the training stimuli. They acquired a serial-probe-recognition (SPR) task with variable (1-6) item list lengths. This SPR acquisition, although gradual, was more rapid for the monkeys than for pigeons similarly trained. Testing with a fixed list length of four items at different delays between the last list item and the probe test item revealed changes in the serial-position function: a recency effect (last items remembered well) for 0-s delay, recency and primacy effects (first and last list items remembered well) for 1-, 2-, and 10-s delays, and only a primacy effect for the longest 30-s delay. These results are compared with similar ones from pigeons and are discussed in relation to theories of memory processing.     

Auditory list memory and interference processes in monkeys.

Memory of 2 rhesus monkeys (Macaca mulatta) was tested in a serial probe recognition task with lists of 4 natural or environmental sounds, different retention intervals, and different manipulations of interference. At short retention intervals, increasing the separation of list items reduced the primacy effect and produced a recency effect. Similar results were shown by increasing interference across lists through item repetitions or making the first 2 list items high-interference items. These results indicated that decreasing first-item performance reduced proactive interference on memory of the last list items. At long (20 s) retention intervals, making the last list items of high interference reduced the recency effect, reduced retroactive interference, and produced a primacy effect. Taken together, interference plays a role in determining the primacy and recency effects of the serial-position function.     

Visual list memory in capuchin monkeys (Cebus apella)

Memory of 3 capuchin monkeys, Cebus apella, was tested with lists of 4 travel-slide pictures and different retention intervals. They touched different areas of a video monitor to indicate whether a test picture was in a list. At short retention intervals (0 s, 1 s, 2 s), memory was good for the last list items (recency effect). At a 10-s retention interval, memory improved for 1st list items (primacy effect). At long retention intervals (20 s and 30 s), primacy effects were strong and recency effects had dissipated. The pattern of retention-interval changes was similar to rhesus monkeys, humans, and pigeons. The time course of recency dissipation was similar to rhesus monkeys. The capuchin's superior tool-use ability was discussed in relation to whether it reflects a superior general cognitive ability, such as memory. In terms of visual memory, capuchin monkeys were not shown to be superior to rhesus monkeys.     

A primacy effect in monkeys when list position is relevant

In Experiment 1 (1a and 1b), Rhesus monkeys (Macaca mulatta) learned lists of two-choice visual discriminations in which list position was relevant to discrimination performance. For example, Stimulus A was the rewarded stimulus if it was presented at List Position 1, but was not rewarded if it was presented at any other position in the list; similarly, Stimulus B was rewarded only at List Position 2, and so on. In learning these lists, all animals showed a marked primacy effect. In Experiment 2 (2a and 2b), Rhesus monkeys and Cynomolgus monkeys (M. fascicularis) learned lists of visual discriminations in which each visual stimulus occupied a fixed position in a list, but list position was not relevant to discrimination performance. For example, Stimulus E was always rewarded, and was always presented at List Position 1. To increase the salience of list beginning as a distinctive event, successive presentations of the list were separated by 24-hr intervals. In Experiment 2 there was no primacy effect, however. These results show for the first time that a primacy effect can be obtained in visual discrimination learning by monkeys. Furthermore, they suggest that it is obtained only when list position is relevant to the discrimination learning task.     

Serial position phenomena: Training and retrieval effects

With successive free recall lists primacy items are usually among the first to be reported on the initial list. Recency items will then take over and be first reported on later lists. This retrieval shift was studied under varied list conditions designed to counteract ordinary position effects, and proved to be a stable and resistent effect. One experiment had subjects practice on five different free recall lists over three trials, and the results agreed with the hypothesis that primacy reduction is caused by proactive interference rather than by the primacy to recency report shift. Experiments of the usual one-session laboratory type have consistently failed to show practice effects on serial lists with incompatible spatial and temporal order cues. In a case study of five subjects examined over a period of three months only slight improvement on single-trial lists was observed. However, when naive subjects were given four successive trials with the same type of cue-conflict list, prominent practice effects were easily demonstrated. Observations confirmed the assumption that repeated presentations of items located in middle list positions may counteract the privilege of primacy and recency positions. When repetitions were made within contracting and expanding lists, the results proved that active anchoring, making itself visible as primacy effects, is feasible with contracting lists but difficult with expanding lists. Active performance of list learning strategies generally results in primacy effects; whereas passive shortcut procedures, in learning and retrieval of information, produce recency effects. Predominant recency effects are symptoms of difficult task situations only partially mastered by the learner; primacy effects point to more successful elaboration. Overall, serial position effects do not seem to be due to structural memory stores so much as to the working of cognitive strategy factors. A problem-solving theory was presented as an alternative to information-processing models of serial learning and memory.     

Recency judgments as a function of word frequency: A framing effect and frequency misattributions

The effects of word frequency on judgments of recency of item presentation were examined in two experiments. Subjects in Experiment 1 were presented two mixed lists of high- and low-frequency words followed by a list assignment task for recognized items. It was found that subjects were biased toward assigning low-frequency words to the more recently presented list. Subjects in Experiment 2 were presented a single mixed list of high- and low-frequency words followed by either a relative recency of presentation judgment task or a relative primacy of presentation judgment task. Each word pair on the tests contained one high-frequency word and one low-frequency word. It was found that, for the recency judgment task, subjects were biased to select the low-frequency item as having been presented more recently. However, on the parallel primacy judgment task, there were no effects of word frequency; moreover, overall accuracy levels were higher with primacy than with recency instructions. We interpret the effects of word frequency on recency judgments in Experiments 1 and 2 in terms of a misattribution of frequency-related differences in recollection-based recognition. The finding that recency and primacy instructions produced different patterns of results provides further evidence (Flexser & Bower, 1974) for an effect on performance of the way in which the temporal judgment task was framed.     

Short-Term Visual Recognition Memory in Pigeons

Recognition memory for lists of items was investigated in pigeons using a YES-NO recognition technique. Experiment I showed that increasing the exposure duration of the first item of a two-item list improved recognition for that item without impairing recognition of the second item. Experiment II showed that decreasing the inter-trial interval had no effect on correct YES responses but significantly increased the number of false YES responses. Experiment III showed that recognition for the last two items of a three-item list was no poorer than that for lists of only two items. Experiment IV showed that increasing the delay between presentation and test of a two-item list (from 0·25-1 s) had a more disruptive effect on recognition for the second than for the first item. The data from these four experiments support a model proposed by Roberts and Grant, according to which memory traces are independent, and decay as a negatively accelerated function of time. Experiments V, VI, and VII investigated recognition for lists of three, four, and five items, and found no evidence for a primacy effect, performance being a linear function of time since sample offset.     

Evidence for similar principles in episodic and semantic memory: The presidential serial position function

When people recall a list of items that they have just experienced (an episodic memory task), the resulting serial position function looks strikingly similar to that observed when people are asked to recall the presidents of the United States (a semantic memory task). Despite the similarity in appearance, there is disagreement about whether the two functions arise from the same processes. A local distinctiveness model of memory, SIMPLE, successfully fit the presidential data using two underlying dimensions: one corresponding to item (or presidential) distinctiveness and the other to order (or positional) distinctiveness. According to the model, presidential primacy and recency are due to the same mechanisms that give rise to primacy and recency effects in both shortand long-term episodic memory. All of these primacy and recency effects reflect the relative distinctiveness principle (Surprenant & Neath, 2009): Items will be well remembered to the extent that they are more distinct than competing items at the time of retrieval.     

Primacy and recency effects in nonhuman primates.

The reports of primacy and recency memory effects in nonhuman primates have been criticized because they have all used an initiating response. That is, the presentation of the to-be-remembered list of items was always contingent on a response being initiated by the nonhuman primate. It has been argued that this initiating response improves performance for early items in the list, resulting in the occurrence of the primacy effect, independent of any memory processing mechanism. This criticism was addressed in the present study by not using an initiating response prior to the presentation of the list. Nevertheless, both a primacy and a recency effect were observed in all 6 rhesus monkeys evaluated using a serial probe recognition task. Thus, the results are similar to those for humans, in that both primacy and recency effects can be obtained in nonhuman primates. A brief literature review is included, and it is proposed that the primacy and recency effects observed in humans, nonhuman primates, and infraprimates can be explained within the context of the configural-association theory.     

Free recall and complexity of pictorial stimuli

In order to explore variables underlying primacy and recency effects in free recall of pictorial material, norms were developed using 120 subjects who rated the vividness and complexity of slides. Two experiments were then run in which two levels of each of these variables (extreme high and low ratings) were factorially combined. In the first experiment 24 subjects were shown three mixed lists, two short and one long (consisting of materials of all four combinations of vividness and complexity), and in the second experiment 12 subjects were shown four pure lists (consisting of materials of a single type). Analysis of variance showed list length in the mixed list experiment and complexity in both experiments to be strong determinants of recall. Greatest recall was for items of low complexity in short lists. Weak, but statistically significant, serial position effects were evident, particularly for less complex items. The effects of primacy and recency seem to decrease with increasing complexity of visual materials, perhaps because of the greater difficulty in rehearsing more complex pictures either verbally or iconically.     

Serial position effects in implicit memory for multiple-digit numbers

Serial position effects in implicit and explicit memory were investigated in a short-term memory task. A study list composed of four, spatially distributed, two-digit numbers was presented, followed by an item recognition task (explicit test) and an implicit memory task in which participants were asked to verify a simple addition equation where the presented answer was either primed or not primed by one of the number pairs in the study list. Similar serial position effects were observed in explicit and implicit memory, with faster response times for correct decisions on the first than on the later list positions. The presence of a primacy effect but no recency effect is consistent with previous studies of explicit memory with visual presentation. The results suggest that similar principles of temporal information processing govern priming and episodic short-term memory.     

Serial recall of colors: Two models of memory for serial order applied to continuous visual stimuli

This study investigated the effects of serial position and temporal distinctiveness on serial recall of simple visual stimuli. Participants observed lists of five colors presented at varying, unpredictably ordered interitem intervals, and their task was to reproduce the colors in their order of presentation by selecting colors on a continuous-response scale. To control for the possibility of verbal labeling, articulatory suppression was required in one of two experimental sessions. The predictions were derived through simulation from two computational models of serial recall: SIMPLE represents the class of temporal-distinctiveness models, whereas SOB-CS represents event-based models. According to temporal-distinctiveness models, items that are temporally isolated within a list are recalled more accurately than items that are temporally crowded. In contrast, event-based models assume that the time intervals between items do not affect recall performance per se, although free time following an item can improve memory for that item because of extended time for the encoding. The experimental and the simulated data were fit to an interference measurement model to measure the tendency to confuse items with other items nearby on the list—the locality constraint—in people as well as in the models. The continuous-reproduction performance showed a pronounced primacy effect with no recency, as well as some evidence for transpositions obeying the locality constraint. Though not entirely conclusive, this evidence favors event-based models over a role for temporal distinctiveness. There was also a strong detrimental effect of articulatory suppression, suggesting that verbal codes can be used to support serial-order memory of simple visual stimuli.     

Interference processes in monkey auditory list memory

A rhesus monkey’s memory was tested for single items and four-item lists of natural and environmental sounds. Memory items were presented from a center speaker, followed by a retention delay and then a choice response to a test sound presented simultaneously from two side speakers. Recognition of the last item of four-item lists was much poorer than that of single items at 0-, 1-, and 2-sec delays, despite there being the same temporal relations between study and test. This result showed that the first three items proactively interfered with memory of the last list item. Proactive interference dissipated after 2 sec, revealing a recency effect that eventually equaled single-item performance. Recognition of the first item of four-item lists was much poorer than single items at 20- and 30-sec delays, showing that the last three items retroactively interfered with memory of the first list item. The results point to the critical nature of interference processes in the understanding of serial position functions.     

Enumeration produces poor primacy for tactile presentation relative to visual and auditory presentation as the only modality effect

Methodological biases may help explain the modality effect, which is superior recall of auditory recency (end of list) items relative to visual recency items. In 1985 Nairne and McNabb used a counting procedure to reduce methodological biases, and they produced modality-like effects, such that recall of tactile recency items was superior to recall of visual recency items. The present study extended Nairne and McNabb's counting procedure and controlled several variables which may have enhanced recall of tactile end items or disrupted recall of visual end items in their study. Although the results of the present study indicated general serial position effects across tactile, visual, and auditory presentation modalities, the tactile condition showed lower recall for the initial items in the presentation list than the other two conditions. Moreover, recall of the final list item did not differ across the three presentation modalities; modality effects were not found. These results did not replicate the findings of Nairne and McNabb, or much of the past research showing superior recall of auditory recency items. Implications of these findings are discussed.     

KNOWLEDGE OF THE ORDINAL POSITION OF LIST ITEMS IN RHESUS MONKEYS

Abstract —What is learned during mastery of a serial task: associations between adjacent and remote items, associations between an item and its ordinal position, or both? A dear answer to this question is lacking in the literature on human serial memory because it is difficult to control for a "naive" subject's linguistic competence and extensive experience with serial tasks. In this article, we present evidence that rhesus monkeys encode the ordinal positions of items of an arbitrary list when there is no requirement to do so. First, monkeys learned four nonverbal lists (1–4). each containing four novel items (photographs of natural objects). The monkeys then learned four 4-item lists that were derived exclusively and exhaustively from Lists 1 through 4, one item from each list. On two derived lists, each item s original ordinal position was maintained. Those lists were acquired with virtually no errors. The two remaining derived lists, on which the original ordinal position of each item was changed, were as difficult to learn as novel lists. The immediate acquisition of lists on which ordinal position was maintained shows that knowledge of ordinal position can develop without the benefit of language, extensive list-learning experience, or explicit instruction to encode ordinal information.     

Immediate recognition memory for wine

We describe a preliminary investigation concerning the short-term recognition memory function for gustatory stimuli (wines). In Experiment 1A, 24 non-expert wine drinkers completed a yes/no recognition task for 3-wine sequences. For the raw recognition scores, the serial position function comprised both primacy and recency. Recency did not, however, achieve significance for the d′ scores. In Experiment 1B, 24 participants completed the same yes/no recognition task for 3-visual matrix sequences. In contrast to Experiment 1A, the serial position function comprised recency and an absence of primacy. We argue that the presence of primacy for the wine sequences cannot be interpreted via a verbal labelling strategy, nor can it be interpreted via proactive interference from the first wine in the list on subsequent list items. The result suggests qualitative differences in the memory processing for gustatory and non-verbal visual stimuli.     

A recency-based account of the list length effect in free recall

Free recall was examined using the overt rehearsal methodology with lists of 10, 20, and 30 words. The standard list length effects were obtained: As list length increased, there was an increase in the number and a decrease in the proportion of words that were recalled. There were significant primacy and recency effects with all list lengths. However, when the data were replotted in terms of when the words were last rehearsed, recall was characterized by extended recency effects, and the data from the different list lengths were superimposed upon one another. These findings support a recency-based account of episodic memory. The list length effect reflects the facts that unrehearsed words are less recent with longer lists, and that with longer lists, a reduced proportion of primacy and middle items may be rehearsed to later positions.