Rehearsal grouping and hierarchical organization of serial position cues in short-term memory

Lists of 8, 9, or 10 digits were presented at the rate of 1 digit/sec. to subjects instructed to rehearse silently the digits in non-overlapping groups of 1, 2, 3, 4, or 5 digits, after hearing each digit. Subjects were instructed not to rehearse any digits outside the group currently being presented. Rehearsing in 3's was optimal, irrespective of list length. Both recall of items and recall of the correct positions of items improved from 1's to 2's to 3's. Recall of items declined very little from 3's to 4's to 5's, but recall of position declined sharply. Errors in positioning digits tended, above chance, to be in the same group or the same position in a different group. The results suggest that both item-to-item associations and serial positin-to-item associations are formed in short-term memory, that only two or three serial position cues are used, but that these serial position cues can be hierarchically organized into a beginning, middle, and end group and a beginning, middle, and end position within a group.     

Rate of presentation in running memory and direct manipulation of input-processing strategies

An experiment was carried out to examine the effect of presentation rate on recall, as a function of the kind of input-processing carried out by the subject during a running memory task. Subjects listened to long sequences of digits (16-35 items in length), and attempted to recall as many as possible of the last 10 items presented during a 15 s break between successive sequences. Digits were presented at rates of 1, 2 or 3/s in different sequences, distributed randomly throughout a 60-sequence test. Separate groups of 16 subjects were instructed to use one of the following strategies in listening to the digits: Active--rehearsing and grouping digits by threes; Passive--avoiding all forms of organization of the input. The results demonstrate clear and reliable differences between strategies in the effect of rate. Active is best at 1/s and deteriorates monotonically with increases in rate, while Passive shows the opposite trend, improving from 1 to 3/s. The operation of an important input-processing factor is evident in these findings, and is probably at least partly responsible for the previous lack of agreement in studies of the effect of presentation rate in immediate recall.     

Response elimination in rats with schedules of omission training, including yoked and response-independent reinforcement comparisons

After rats were trained to lever press, response elimination began with factorial combinations of fixed vs variable and adjusting vs constant omission training schedules. A time interval scheduling reinforcement remained the same in a constant schedule, and its length was increased as response rate declined in the adjusting schedule. A variable time (VT) response-independent reinforcement schedule followed response elimination to test the durability of response cessation. Experiment I included groups whose reinforcement was yoked to that received by the omission schedule groups. Rate of response elimination was faster with an adjusting than a constant schedule, and slightly faster with a variable than a fixed schedule. There were no significant differences in rate of response elimination between omission schedule and yoked groups. Shorter delay of reinforcement tended to increase rate of response elimination. In the subsequent VT durability test all groups displayed near-zero response rates. In Experiment II adjusting fixed and variable omission schedules, including yoked groups, were compared with fixed time (FT) and VT reinforcement schedules. Response elimination was slower in the FT and VT groups, and they responded more in a subsequent VT durability test. It was concluded that differential reinforcement of other behavior fails to account for these omission training effects, and suggestions were made for an analysis based on the correlation between response and reinforcement rate.     

Spatial and temporal task characteristics as stress: a test of the dynamic adaptability theory of stress, workload, and performance

The goal for this study was to test assertions of the dynamic adaptability theory of stress, which proposes two fundamental task dimensions, information rate (temporal properties of a task) and information structure (spatial properties of a task). The theory predicts adaptive stability across stress magnitudes, with progressive and precipitous changes in adaptive response manifesting first as increases in perceived workload and stress and then as performance failure. Information structure was manipulated by varying the number of displays to be monitored (1, 2, 4 or 8 displays). Information rate was manipulated by varying stimulus presentation rate (8, 12, 16, or 20 events/min). A signal detection task was used in which critical signals were pairs of digits that differed by 0 or 1. Performance accuracy declined and workload and stress increased as a function of increased task demand, with a precipitous decline in accuracy at the highest demand levels. However, the form of performance change as well as the pattern of relationships between speed and accuracy and between performance and workload/stress indicates that some aspects of the theory need revision. Implications of the results for the theory and for future research are discussed.     

Effects of short-term memory contents on short-and long-term memory searches

The Ss memorized a long-term set (LT set) of 20 words before participating in a recognition memory test. On each trial Ss were given a new short-term set (ST set) of from one to four words or one to four digits. The Ss gave a positive response to a test item that was a member of either the ST or the LT set and gave a negative response to a test item not in either set; both words and digits were used as test stimuli. The results indicated that reaction time (RT) to positive test items from the ST set was an increasing function 0f the size of the ST set; the same was also true for negative responses to test digits when the ST set was composed of digits. RT to other test stimuli, however, did not depend on ST set size. These results are consistent with the view that Ss access long-term memory (LTM) and short-term memory (STM) simultaneously rather than sequentially. The results also showed that Ss responded more quickly to test items from the LT set when the ST set contained digits than when it contained words. Negative test items that were words, however, were rejected more slowly when the ST set contained digits than when it contained words. These results suggest that the search of LTM was affected by the contents of STM.     

Phonemic vowel length contrasts in cerebellar disorders

Apraxia of speech and Broca's aphasia both affect voice onset time (VOT) whereas phonemic vowel length distinctions seem to be preserved. Assuming a close cooperation of anterior perisylvian language zones and the cerebellum with respect to speech timing, a similar profile of segment durations must be expected in ataxic dysarthria. In order to test this hypothesis, patients with cerebellar atrophy or cerebellar ischemia were asked to produce sentence utterances including either one of the German lexial items "Rate" (/ra:t(h)e/, 'installment'), "Ratte" (/rat(h)e/, 'rat'), "Gram" (/gra:m/, 'grief'), "Gramm" (/gram/, 'gramm'), "Taten" (/t(h)atn/, 'actions'), or "Daten" (/datn/, 'data'). At the acoustic signal, the duration of the target vowels /a/ and /a:/ as well as the VOT of the word-initial alveolar stops /d/ and /t/ were determined. In addition, a master tape comprising the target words from patients and controls in randomized order was played to three listeners for perceptual evaluation. In accordance with a previous study, first, the cerebellar subjects presented with a reduced categorical separation of the VOT of voiced and unvoiced stop consonants. Second, vowel length distinctions were only compromised in case of the minimal pair "Gram"/"Gramm." In contrast to "Rate"/"Ratte", production of the former lexical items requires coordination of several orofacial structures. Disruption of vowel length contrasts would, thus, depend upon the complexity of the underlying articulatory pattern.     

Repetition priming in simple addition depends on surface form and typicality

Repetition priming and recognition memory for numbers were measured in four experiments using single-digit addition. Results of the first two experiments indicate that when numbers were presented as number words and dot configurations, preexposure of the same problem in the same notation produced greater reaction-time benefit than did preexposure of the same problem in Arabic-digit notation. In contrast, when numbers were presented as Arabic digits, preexposure of the same problem in Arabic digit, number word, and dot notation produced the same amount of priming. In the third experiment, priming was shown to be greatest, for all three notations, when the task performed on preexposure trials (addition or multiplication) matched the task performed on repetition trials (addition). Results of the fourth experiment, measuring recognition memory, were comparable to the priming results in the sense that memory was superior when notation matched across repetitions if the test involved number words and dot configurations but not Arabic digits. These data are interpreted in terms of models of numerical cognition, and they support the hypothesis that the influence of surface form on repetition priming depends on the typicality of the input for the task.     

Need probability affects retention: A direct demonstration

Recent memory theory has emphasized the concept ofneed probability—that is, the probability that a given piece of learned information will be tested at some point in the future. It has been proposed that, in real-world situations, need probability declines over time and that the memory-loss rate is calibrated to match the progressive reduction in need probability (J. R. Anderson & Schooler, 1991). The present experiments were designed to examine the influence of the slope of the need-probability curve on the slope of the retention curve. On each of several trials, subjects memorized a list of digits, then retained the digits in memory for 1, 2, 4, 8, or 16 sec. Some trials ended with a recall test; other trials ended with the message, “no test.” In Experiment 1, the likelihood of encountering a memory test (i.e., the need probability) was made to either increase or decrease as the retention interval increased; in Experiment 2, need probability either was flat (invariant across retention intervals) or decreased as the retention interval increased. The results indicated that the shape of the need-probability curve influenced the slope of the retention curve (Experiment 1) and that the effect became larger as the experimental session progressed (Experiment 2). The findings support the notion that memory adapts to need probabilities and that the rate of forgetting is influenced by the slope of the need-probability curve. In addition, all of the forgetting curves approximated a power function, suggesting that need probability influences the slope but not the form of forgetting.     

Cognitive addition: strategy choice and speed-of-processing differences in young and elderly adults

Sixty young and 60 elderly adults completed a pencil-and-paper addition test and solved 40 computer-presented simple addition problems. Strategies and problem solution times were recorded on a trial-by-trial basis and were classified in accordance with the distributions of associations model of strategy choices. The elderly group showed a performance advantage on the ability measure and for the developmental maturity of the mix of problem-solving strategies, but the young group showed an advantage for overall solution times. A componential analysis of the overall solution times for memory retrieval trials, however, showed no reliable age difference for rate of retrieving addition facts from long-term memory but did suggest that the elderly adults might have been slower than the younger adults for rate of encoding digits and verbally producing an answer. Overall results are interpreted within the context of the strategy choice model.     

Simple and conditional discriminations in rats: The effects of delays and scopolamine

In simple delayed discriminations (DD), the reinforcer depends on information available from the sample stimulus, whereas in delayed conditional discriminations (DCD), the reinforcer depends on information jointly available from the sample and the test stimuli. The present experiments compared performance in rats trained in DD and DCD (a) during acquisition over training sessions, and as a function of increasing (b) delay in the memory interval and (c) dosage with the anticholinergic scopolamine. In this work, clicks and tones served as sample stimuli, and bright and dim overhead lights served as test stimuli for lever pressing for food during the test stimulus. The DD task was acquired more rapidly and was more resistant to the effects of delay between the sample and test stimuli. These results replicate previous work with pigeons. In addition, the dose-performance function of scopolamine differed between DD and DCD. Performance declined as a linear function of drug dose in the DCD group. In contrast, performance declined abruptly as a stepwise function of drug dose in the DD group. These latter results suggest that the cholinergic system may be utilized differently during DD and DCD.     

Cognitive arithmetic: comparison of operations

Adults' performance of simple arithmetic calculations (addition, multiplication, and numerical comparison) was examined to test predictions of digital (counting), analog, and network models. Although all of these models have been supported by studies of mental addition, each leads to a different prediction concerning relations between the times required for addition, multiplication, and numerical comparison. Pairs of single-digit integers were presented and reaction times (RTs) for adding, multiplying, and comparing the stimuli were collected. A high correlation between RT for addition and multiplication of the same digits was obtained. This result is consistent with a network model, but presents difficulties for both analog and counting models. A "ties" effect of no increase in RT with increases in problem size for doubles such as 2 + 2 has been found in previous studies of addition using verification procedures, but was not found with the production task employed in the present study. Instead, a different kind of ties effect was found. Reaction time for both addition and multiplication of ties increased more slowly with problem size than did RT for non-tie problems. This ties effect, and the finding that probability of making errors contributes independently of problem size to RT support a distinction between location and accessibility of information in a network.     

Corsi's block-tapping test: some characteristics of the spatial path which influence memory

By using a sequence of digits it is possible to indicate the path of Corsi's block-tapping test by drawing a line to join the central points of the cubes which make up the sequence. By doing this one can analyze the sequence of digits according to quantitative parameters. There were three characteristics of the spatial path taken into consideration in this research: the number of cubes which constitute a series of digits, the number of times the path intersected itself, and the length of the path measured in millimeters. The experiment, carried out with 70 university students, showed that all three factors were significant on analysis of variance, and also that there were differences between the sexes, the men performing better. No interactions were significant. Despite this, additional significant differences were found among the series with the same number of cubes, intersections, and length, meaning that other variables influence the difficulty of the spatial path.     

A strict test of the phonological loop hypothesis with Libyan data

In Arabic, there are two ways, differing in length, of pronouncing each digit. This feature of word pairs that are conceptually identical but of different length allows for a stricter test of the phonological loop hypothesis than has been reported previously. Libyan schoolchildren, both boys and girls, of two grades took part in a quasi-experimental study in which shorter and longer digits and shorter and longer words were presented in recall and pronunciation tasks. The results confirmed the validity of the phonological loop model in that memory span was longer for shorter stimuli. Analysis of the data with structural equation modeling showed that only 17% of the individual-level variation in memory span could be explained by pronunciation speed. In an analysis of covariance, it was determined that pronunciation speed could account for a substantial proportion of the variation found across age (8-year-olds vs. 10-year-olds), stimulus modality (digits vs. words), and stimulus length (short vs. long), but not for gender differences.     

Short term retention of sentences

A series of experiments was performed on the interaction between the short-term retention of sentences and of digits. In Experiment I a digit span method was used whereby subjects were presented with a sentence followed by a sequence of digits and were required either (a) to recall the sentence first and then the digits or (b) to recall the digits followed by the sentence. Under condition (a) prior recall of the sentence reduced the percentage of digit sequences correctly recalled, while under condition (b) retention of the sentence appeared to have no effect on digit recall. This last finding was confirmed in Experiment II, where the sentences varied both in grammatical complexity and length.

In Experiment III the effect of prior recall of a sentence on the recall of digits was found to depend on the type of sentence used. A correlation was observed between the size of this effect and the time taken to recall a sentence. The rate of forgetting suggested by this observation was comparable to that obtained in Experiment IV, where subjects performed an intervening task that did not involve immediate memory for sentences in the interval between the presentation and recall of a six-digit sequence.

It was concluded from these results that the short-term retention of sentences and of lists of items cannot be explained in terms of some general store of limited capacity.     

The influence of string length and repetition on chunking of digit strings

This study examined the effects of string length and repetitions on number processing with a data entry task. Participants read and entered strings of between three and eight digits and then typed them on the keypad of a computer. Chunking effects were found for all string lengths, with chunk sizes of as small as two digits. Chunk boundary placement varied depending on the length of a digit string, and chunking was avoided at positions between digit repetitions, even when those positions were otherwise common chunk boundaries. Digit repetitions significantly reduced the study time required to process a string prior to its entry. These results are interpreted as showing that flexible chunking strategies and the presence of repetitions are used to facilitate number processing.Means with an asterisk correspond to repeated digits     

Rapid parallel semantic processing of numbers without awareness

In this study, we investigate whether multiple digits can be processed at a semantic level without awareness, either serially or in parallel. In two experiments, we presented participants with two successive sets of four simultaneous Arabic digits. The first set was masked and served as a subliminal prime for the second, visible target set. According to the instructions, participants had to extract from the target set either the mean or the sum of the digits, and to compare it with a reference value. Results showed that participants applied the requested instruction to the entire set of digits that was presented below the threshold of conscious perception, because their magnitudes jointly affected the participant’s decision. Indeed, response decision could be accurately modeled as a sigmoid logistic function that pooled together the evidence provided by the four targets and, with lower weights, the four primes. In less than 800 ms, participants successfully approximated the addition and mean tasks, although they tended to overweight the large numbers, particularly in the sum task. These findings extend previous observations on ensemble coding by showing that set statistics can be extracted from abstract symbolic stimuli rather than low-level perceptual stimuli, and that an ensemble code can be represented without awareness.     

Reading Rates and Digit Span in Bilinguals: The Superiority of Mother Tongue

Several studies have shown a negative linear relationship between speech rate and memory span. This relationship has implications for bilingual studies, as span could be larger in a bilingual's secondary language provided that pronunciation rate is faster than in the mother language. The purpose of this study was to investigate the effects of digit word length on digit span in bilinguals. Experiment 1 tested the effects of digit syllable length on speech rate in five different bilingual groups. Results revealed that digit-reading rates were significantly faster in all mother languages. Experiment 2 examined more closely the correspondence between speech rate and digit span with Portuguese-English bilinguals. Results showed that digit-reading rates were faster and digit span larger in the mother language even if the mean number of syllables per digit was higher. The superiority of mother tongue was discussed according to the view that digits are subject to massive practice in one's native language with a strong tendency to be abbreviated, thus reducing its spoken duration.     

Object Size as a Determinant of Grasping in Infancy

The early development and patterns of development of prehensile ability were examined. Infants 5, 7, and 9 months old were presented five objects, 0.5, 1.0, 3.5, 7.0, and 14.0 cm in diameter. The findings revealed that infants as young as 5 months old were able to differentiate grip configurations as a function of object size. The number of grasps involving the two or three most radial digits (thumb, index finger, and long finger) increased greatly over this age span. At 9 months of age these kinds of grasps were 10 times more frequent than at 5 months of age. However, at each age level, when only the two or three most radial digits were used, the reaches were typically directed at the two smallest objects. These findings suggest that it was not a perceptual problem that the younger infants were facing, nor was the problem knowing when to use different kinds of grasps; rather, the problem was one of cortico-motoneural connections, which are better established in older infants. The findings also suggest that traditionally described sequential development of infants' prehension is rigid and conservative. The discrepancy with earlier results may also be attributed to the difference in the objects' sizes and the way they were presented.     

Interactive effects of numerical surface form and operand parity in cognitive arithmetic

In Experiment 1, adults (n = 48) performed simple addition, multiplication, and parity (i.e., odd-even) comparisons on pairs of Arabic digits or English number words. For addition and comparison, but not multiplication, response time increased with the number of odd operands. For addition, but not comparison, this parity effect was greater for words than for digits. In Experiment 2, adults (n = 50) solved simple addition problems in digit and word format and reported their strategies (i.e., retrieval or procedures). Procedural strategies were used more for odd than even addends and much more for word than digit problems. The results indicate that problem encoding and answer retrieval processes for cognitive arithmetic are interactive rather than strictly additive stages.     

Force gradients in stimulus generalization

Pigeons were trained to peck with differing force requirements on a key specially designed to measure and control force of pecking without changes in the mechanical threshold. Following training on a key illuminated by a single wavelength, a generalization test was given. Force and rate gradients were obtained. Force gradients were shown to have a form similar to rate gradients. The slope of the force gradients was a direct function of the force of responding at the conclusion of training. Rate gradients were independent of the force of responding.