Serial list combination by monkeys (Macaca mulatta): test cues and linking

This investigation assessed prospective bases of non-human primate cognitive operations that support serial list memory. Four macaques learned 3-, 5-item ordered lists of objects (as two-choice problems) and then either did or did not (in a within-subject design) receive training on pairs that linked the three original lists into a 15-item serial order. Next, subjects experienced selective exposure trials on object pairs that either maintained or contrasted to the serial position relationships seen during original learning. Subsequent comprehensive tests assessed the interactive effects of linking and exposure conditions on choosing in accord with a combined 15-item serial order. Linking readily induced monkeys to merge lists into a 15-item order, but restricting early exposure to pairs with the same positional relationships as original training slowed, but did not prevent, list combination. Exposure to positional relationships congruent with the combined (15-item) list and different from those of original 5-item training aided both expression of the linking effect and acquisition after no link training. Thus, list linking facilitated serial reorganization by inducing release from error derived from memory for prior learned positional relationships. The task was recommended as a prospective evaluator of continuity of cognitive processes among species.     

Neuroanatomical correlates of category-specific semantic disorders: A critical survey

Current models of verbal short‐term memory (STM) propose various mechanisms for serial order. These include a gradient of activation over items, associations between items, and associations between items and their positions relative to the start or end of a sequence. We compared models using a variant of Hebb's procedure in which immediate serial recall of a sequence improves if the sequence is presented more than once. However, instead of repeating a complete sequence, we repeated different aspects of serial order information common to training lists and a subsequent test list. In Experiment 1, training lists repeated all the item–item pairings in the test list, with or without the position–item pairings in the test list. Substantial learning relative to a control condition was observed only when training lists repeated item–item pairs with position–item pairs, and position was defined relative to the start rather than end of a sequence. Experiment 2 attempted to analyse the basis of this learning effect further by repeating fragments of the test list during training, where fragments consisted of either isolated position–item pairings or clusters of both position–item and item–item pairings. Repetition of sequence fragments led to only weak learning effects. However, where learning was observed it was for specific position–item pairings. We conclude that positional cues play an important role in the coding of serial order in memory but that the information required to learn a sequence goes beyond position–item associations. We suggest that whereas STM for a novel sequence is based on positional cues, learning a sequence involves the development of some additional representation of the sequence as a whole.     

Serial learning by rhesus monkeys: II. Learning four-item lists by trial and error

Three rhesus macaque monkeys were trained to produce novel 4-item lists (A-->B-->C-->D) on which all items were displayed from the start of training. Subjects were previously trained to produce 4-item lists by adding one item at a time (A, A-->B, A-->B-->C, and A-->B-->C-->D; lists K. B. Swartz et al., 1991). Those lists could be mastered by responding to each new item last. To learn lists on which all items were displayed from the start of training, subjects had to recall the consequences of errors and correct responses to each item. Errors ended the trial; correct responses to A, B, or C allowed the trial to continue. A correct response to D produced food reward. Although the probability of executing a 4-item list correctly by chance was .04, each subject mastered 4 novel 4-item lists by trial and error. The ability of monkeys to use a trial-and-error strategy to learn novel lists provides a basis for studying the development of serial expertise in animals.     

Cognitive imitation in 2-year-old children (<Emphasis Type="Italic">Homo sapiens</Emphasis>): a comparison with rhesus monkeys (<Emphasis Type="Italic">Macaca mulatta</Emphasis>)

Here we compare the performance of 2-year-old human children with that of adult rhesus macaques on a cognitive imitation task. The task was to respond, in a particular order, to arbitrary sets of photographs that were presented simultaneously on a touch sensitive video monitor. Because the spatial position of list items was varied from trial to trial, subjects could not learn this task as a series of specific motor responses. On some lists, subjects with no knowledge of the ordinal position of the items were given the opportunity to learn the order of those items by observing an expert model. Children, like monkeys, learned new lists more rapidly in a social condition where they had the opportunity to observe an experienced model perform the list in question, than under a baseline condition in which they had to learn new lists entirely by trial and error. No differences were observed between the accuracy of each species' responses to individual items or in the frequencies with which they made different types of errors. These results provide clear evidence that monkeys and humans share the ability to imitate novel cognitive rules (cognitive imitation).     

Linking of serially ordered lists by macaque monkeys (Macaca mulatta): list position influences

Five monkeys (Macaca mulatta) were trained on 2 sets of 3 5-item serially ordered lists. Then, each set was either linked or not in a counterbalanced, within-subject design. Linking entailed training on the 2 pairs that ordered the 3 5-item lists into a single overall 15-item series. Choices on novel pairings after linking conditions attempted to define the unique contributions of knowledge of within-list ordinal position and between-lists link training. With linkage, the series was immediately treated as a 15-item ordered list. Without linkage, choices reflected list positions from initial learning, but continued testing with directional reward yielded gradual ordering into a 15-item list. Apparently, monkeys remembered and used initial list-position information, but linkage allowed inference of an integrated serial relationship among items. Results supported primate list memory as an organizational process.     

Ordinal-list integration for symbolic, arbitrary, and analog stimuli by rhesus macaques (Macaca mulatta)

Two numeral-trained monkeys learned to produce 3 5-item lists of Arabic numerals, colors, and arbitrary signs in the correct sequence. The monkeys then responded at above-chance levels when the authors tested them with nonrewarded pair-wise comparisons of items from different lists, indicating their use of ordinal-position information. The authors also tested the monkeys with nonrewarded pair-wise comparisons of an analog quantity and an item from 1 of the 3 learned lists. Although the monkeys were not trained to serially order analog quantities, 1 monkey correctly integrated the analog quantities with the lists of numerals, colors, and signs. The consistent use of an ordinal rule, despite different types of training and varying degrees of experience with the 4 types of stimuli, suggested that the monkey had a robust concept of ordinality.     

Serial learning by rhesus monkeys: I. Acquisition and retention of multiple four-item lists.

Two rhesus monkeys were trained to learn eight 4-item lists, each composed of 4 different photographs. Lists were trained in successive phases: A, A----B, A----B----C, and A----B----C----D. After List 4, retention, as measured by the method of savings, was, on average, 66% (range: 44-84%). Indeed, all 4 lists could be recalled reliably during a single session with neither a decrement in accuracy nor an increase in the latency of responding to each item. Response latencies on a subset test employing all possible 2- and 3-item subsets of each 4-item list support the hypothesis that monkeys form linear representations of a list. Latencies to Item 1 of a subset varied directly with the position of that item in the original list. On List 1, latencies to Item 2 varied directly with the number of intervening items between Item 1 and Item 2 in the original list. During the acquisition of Lists 5-8, both Ss mastered the A----B and A----B----C phases of training in the minimum number of trials possible.     

Retrieval processes for serial order information

Three experiments sought to specify how list structure and rehearsal pattern influence the retrieval of well-learned serial order information. Subjects learned a serial list of 12 words followed by a probed recall task measuring response time. Adjacent list items served as retrieval cues to permit probing of an item by cues which maintained or crossed semantic or rehearsal boundaries. Evidence for structure in serial recall was inferred from the large cue format effects on response time. Such effects were found to be consistent with the semantic relationships in categorized lists and the acquisition rehearsal pattern in unrelated lists. When rehearsal grouping and semantic relatedness were in conflict. the cue format effects conformed mainly to the rehearsal pattern. Extended practice over five sessions did not eliminate these effects for many of the serial items. These results suggest that the structure of the serial list. whether based on previous associations or present rehearsal patterns. can provide a basis for retrieval. A hierarchical search model based on item and order information provided good fits of the data. The model suggested that response time varies with cue formats because cues differ in their efficiency at directing search to the correct response in the list structure. The structure. which is acquired at the time of learning. determines cue efficiency and. hence. the subsequent effects upon response time.     

An experimental analysis of memory processing

Rhesus monkeys were trained and tested in visual and auditory list-memory tasks with sequences of four travel pictures or four natural/environmental sounds followed by single test items. Acquisitions of the visual list-memory task are presented. Visual recency (last item) memory diminished with retention delay, and primacy (first item) memory strengthened. Capuchin monkeys, pigeons, and humans showed similar visual-memory changes. Rhesus learned an auditory memory task and showed octave generalization for some lists of notes--tonal, but not atonal, musical passages. In contrast with visual list memory, auditory primacy memory diminished with delay and auditory recency memory strengthened. Manipulations of interitem intervals, list length, and item presentation frequency revealed proactive and retroactive inhibition among items of individual auditory lists. Repeating visual items from prior lists produced interference (on nonmatching tests) revealing how far back memory extended. The possibility of using the interference function to separate familiarity vs. recollective memory processing is discussed.     

Serial list linking by macaque monkeys (Macaca mulatta): list property limitations

Four sophisticated macaque monkeys (Macaca mulatta) learned 6 different, 15-item ordinal lists (via conditional, 2-choice discriminations) as part of a study assessing some properties of serial list memory in monkeys. After assuring that the first 3 lists were well retained, the researchers attempted to link these by training only the 2 end-item pairs that ordered all 45 items into an inclusive series. A 20-day test of possible pairings among these 45 items was then conducted. Subsequently, the other 3 lists were trained and tested for retention, but no link training was provided. Then, a test like the one that had followed linking was administered. Unlike previous outcomes with three 5-item lists, linking did not yield immediate merger of three 15-item lists into a 45-item list, although 45-item lists were acquired after sufficient exposure to the testing/training regimen under both linking and nonlinking conditions. List length as a limiting factor in linking suggested processing restrictions analogous to those observed in human list memory. Results supported further investigation of list-linking characteristics.     

Chunking during serial learning by a pigeon: II. Integrity of a chunk on a new list

Can a group of items that a pigeon chunks on one list function as such on a second list? In Experiment 1, the ordinal position of the chunk was held constant across both lists. Following training on a list of colors and achromatic geometric forms (A----B----C----D'----E'), the integrity of the color chunk [A----B----C] was maintained on a list of five colors (A----B----C----F----G) even though the basis for establishing that chunk was eliminated. The integrity of the chunk [A----B----C] was also maintained on a new list of colors and forms (A----B----C----D*----E*). In Experiment 2, the ordinal position of a chunk established on list1 (A----B----C'----D') was changed on list 2. As shown by positive transfer between lists 1 and 2, the integrity of the chunks [A----B] and [C'----D'] was maintained on lists X'----A----B----Y' and X'----C'----D'----Y', respectively. Conversely, the heterogeneous list X'----B----C'----Y' took longer to learn than the original list.     

Serial learning with wild card items by monkeys (Cebus apella): implications for knowledge of ordinal position

We investigated monkeys' knowledge of the ordinal positions of stimuli that formed a 5-item serial list, ABCDE, by means of wild card items (W) that could substitute for items in the original series. In Experiment 1, training with wild cards was given on 3-, 4-, and 5-item series. In the last of these series, the wild card substitutions created five wild card sequences, WBCDE through ABCDW. During the final 10 sessions of training with each of two different wild cards (Items x and Y), the 3 subjects were able to successfully complete almost 60% of the wild card sequences. In Experiment 2, the two wild cards were presented on the same trial in 10 different double wild card sequences (e.g., AXCDY). The 2 monkey subjects correctly completed about 59% of the double wild card sequences during the final two training sessions. The performance levels achieved on single and on double wild card sequences, although well below that observed on the baseline sequence ABCDE (90% or better), support the view that the monkeys possessed some knowledge regarding the ordinal position of each baseline item. Consequently, an associative chain interpretation, which does not provide for knowledge of ordinal position, falls short as a complete account of the monkey's capacity for serial learning.     

Serial expertise of rhesus macaques

Here we describe the development of serial expertise in 4 experimentally naive rhesus monkeys that learned, by trial and error, the correct order in which to respond to 3-, 4-, and 7-item lists of arbitrarily selected photographs. The probabilities of guessing the correct sequence on 3-, 4-, and 7-item lists were, respectively, 1/6, 1/24, and 1/5040. Each monkey became progressively more efficient at determining the correct order in which to respond on new lists. During subsequent testing, the subjects were presented with all possible pairs of the 28 items used to construct the four 7-item lists (excluding pairs of items that occupied the same ordinal position in different lists). Subjects responded to pairs from different lists in the correct order 91% of the time on the first trials on which these pairs were presented. These features of subjects' performance, which cannot be attributed to procedural memory, satisfy two criteria of declarative memory: rapid acquisition of new knowledge and flexible application of existing knowledge to a new problem.     

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.     

Position effects in comparative judgments of serial order: List structure vs. differential strength

Two experiments are reported that test the hypothesis that the serial position effect in comparative judgment of ordinal position in arbitrary serial lists results from differential memory or associative strength among list items. The serial position effect in comparative judgment is typically a pattern in which pairs that contain a term from one of the two extremes of the list are processed faster and more accurately than pairs that contain no end terms. The experiments show that a new term added to either the end or the middle of a well-practiced fourterm series behaves almost immediately like the end or central term, respectively, of a well-practiced five-term series. Furthermore, when the added term is removed, the list reverts immediately to the position effect obtained in a four-term series. Theories that explain the position effect by differential build-up of item strength or of interitem associative strength over practice cannot explain these effects. We propose instead that learning of a serial list is accomplished by assigning list members to positions in a general-purpose linear order schema and that subjects can make these assignments rapidly and flexibly.     

Rhythmic groups and subjective chunks in memory for melodies

Memory for brief melodic phrases was tested using a short-term recognition-memory paradigm. The five-note phrases were rhythmically separated from each other and presented in lists four phrases in length. A single five-note test item followed each list and either corresponded rhythmically to one of the phrases as presented in the list (within items) or to the last three notes of one phrase and the first two notes of the next (across items). Within items were easier than across items. Slow presentation (3 notes/sec) was slightly easier than fast (6 notes/see). The J-shaped serial position curve typical of short-term memory for verbal material was obtained. The results support the position that rhythmic grouping of input determines subjective chunking and memory storage, facilitating the recognition of test items chunked in the same way as list items.     

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.     

Conditional recall and the frequency effect in the serial recall task: an examination of item-to-item associativity

The frequency effect in short-term serial recall is influenced by the composition of lists. In pure lists, a robust advantage in the recall of high-frequency (HF) words is observed, yet in alternating mixed lists, HF and low-frequency (LF) words are recalled equally well. It has been argued that the preexisting associations between all list items determine a single, global level of supportive activation that assists item recall. Preexisting associations between items are assumed to be a function of language co-occurrence; HF?CHF associations are high, LF?CLF associations are low, and mixed associations are intermediate in activation strength. This account, however, is based on results when alternating lists with equal numbers of HF and LF words were used. It is possible that directional association between adjacent list items is responsible for the recall patterns reported. In the present experiment, the recall of three forms of mixed lists??those with equal numbers of HF and LF items and pure lists??was examined to test the extent to which item-to-item associations are present in serial recall. Furthermore, conditional probabilities were used to examine more closely the evidence for a contribution, since correct-in-position scoring may mask recall that is dependent on the recall of prior items. The results suggest that an item-to-item effect is clearly present for early but not late list items, and they implicate an additional factor, perhaps the availability of resources at output, in the recall of late list items.     

Knowledge of the ordinal position of list items in pigeons

Ordinal knowledge is a fundamental aspect of advanced cognition. It is self-evident that humans represent ordinal knowledge, and over the past 20 years it has become clear that nonhuman primates share this ability. In contrast, evidence that nonprimate species represent ordinal knowledge is missing from the comparative literature. To address this issue, in the present experiment we trained pigeons on three 4-item lists and then tested them with derived lists in which, relative to the training lists, the ordinal position of the items was either maintained or changed. Similar to the findings with human and nonhuman primates, our pigeons performed markedly better on the maintained lists compared to the changed lists, and displayed errors consistent with the view that they used their knowledge of ordinal position to guide responding on the derived lists. These findings demonstrate that the ability to acquire ordinal knowledge is not unique to the primate lineage. (PsycINFO Database Record (c) 2011 APA, all rights reserved).