Homogeneity computation: How interitem similarity in visual short-term memory alters recognition

Visual short-term recognition memory for multiple stimuli is strongly influenced by the study items’ similarity to one another—that is, by their homogeneity. However, the mechanism responsible for this homogeneity effect has remained unclear. We evaluated competing explanations of this effect, using controlled sets of Gabor patches as study items and probe stimuli. Our results, based on recognition memory for spatial frequency, rule out the possibility that the homogeneity effect arises because similar study items are encoded and/or maintained with higher fidelity in memory than dissimilar study items are. Instead, our results support the hypothesis that the homogeneity effect reflects trial-by-trial comparisons of study items, which generate a homogeneity signal. This homogeneity signal modulates recognition performance through an adjustment of the subject’s decision criterion. Additionally, it seems the homogeneity signal is computed prior to the presentation of the probe stimulus, by evaluating the familiarity of each new stimulus with respect to the items already in memory. This suggests that recognition-like processes operate not only on the probe stimulus, but on study items as well.     

Acoustic interference in a recognition task

Phonetic or acoustic characteristics of stimuli in recall studies have consistently been shown to generate more interference over short intervals than semantic characteristics. We performed three experiments to determine whether this characteristic also applied to recognition processes over short intervals. Subjects were shown study lists of eight words and were asked to recognize which of those words recurred on subsequent eight-word lists. Delays varied from 0 to 100 s between study and test, with a rehearsal-preventing task inserted during the delays. Phonetic distractors generated greater interference than semantic distractors at all delay levels, and semantic distractors generated greater interference than random distractors. These distractor-type differences were not present in long-term recognition tasks. The deterioration in performance over time was considerably slower in these recognition experiments than in previous recall studies.     

Intratrial proactive interference in pigeon short-term memory: Manipulation of stimulus dimension and dimensional similarity

Proactive interference was studied using an intratrial preparation in two delayed matching-to-sample experiments employing pigeons. On interference trials, an interfering sample and a target sample were presented successively and were followed by a test consisting of a choice between two stimuli, one associated with each sample. Control trials were identical to interference trials except that the interfering sample was not presented. On both types of trials, choice of the comparison corresponding to the target sample was defined as correct. Colored fields and line orientations were employed as sample stimuli in Experiment 1, and samples of food and no food and of number of pecks were employed in Experiment 2. Interference was found to be equally robust regardless of whether the interfering and target samples were each selected from any of the four dimensions (color, line orientation, food/no food, or number of pecks). Amount of interference was found to be independent of whether the interfering and target samples employed on a trial were selected from the same dimension or from different dimensions. Evidence was also obtained suggesting that line orientation comparison stimuli are more likely to elicit a response not based on memory than are color comparison stimuli.     

An analysis of interference in recognition memory

A stimulus-sampling model of recognition memory is presented that predicts both proactive and retroactive interference. To test the predictions of the model, a recognition memory experiment was carried out using a standard proactive-retroactive design with a forced-choice task. Both accuracy and latency were measured. The data showed, as predicted, equal proactive and retroactive effects on accuracy, providing solid support for the model. The interference effects are interpreted in terms of the model as arising from an increase in indirect marking, the marking of shared stimulus elements in words other than the study word. The model has two parameters representing the rate of indirect marking for high-frequency and low-frequency words and two parameters reflecting the efficiency of direct marking. The latency results completely paralleled the accuracy findings, showing proactive and retroactive effects. A possible extension of the model to handle latencies is considered.     

Short-term recognition memory for single letters and phonemic similarity of retroactive interference

Copying 12 letters produces more retroactive interference in recognition memory for a single letter when the interference letters possess a vowel sound in common with the letter to be remembered than when they do not. Compared to interference lists that do not include the presented letter, inclusion in the interference list of the letter to be remembered improves recognition memory when the other interference letters have no vowel sound in common with the letter to be remembered, but not otherwise. False recognition rates are greater when the test letter contains a vowel sound in common with the presented letter than when the vowel sounds of these two letters are different. The findings are in complete accord with analogous findings for short-term recall and indicate that short-term recognition memory uses the same phonemic-associative memory system as short-term recall.     

Acoustic and associative coding in short-term memory

Short lists of word-digit pairs were presented to 456 college student subjects. One of the words was repeated as a memory probe either immediately after list presentation or after a short rehearsal interval. The stimulus words were either acoustically identical or associatively related (UP, DOWN). Both acoustic identity and associative relatedness produced a memory decrement which decreased with rehearsal. One interpretation of these results is that the primary memory trace is a multiple-dimension one and that, given time, subjects can recover non-acoustic information from it. The data also indicate that the “fate” over time is different for acoustically similar and associatively related items.     

Proactive interference and item similarity in working memory

Proactive interference (PI) may influence the predictive utility of working memory span tasks. Participants in one experiment (N=70) completed Ravens Advanced Progressive Matrices (RAPM) and multiple versions of operation span and probed recall, modified for the type of memoranda (digits or words). Changing memoranda within- or across-trials released PI, but not doing so permitted PI buildup. Scores from PI-build trials, but not PI-release trials, correlated with RAPM and accounted for as much variance in RAPM as unmodified tasks. These results are consistent with controlled attention and inhibition accounts of working memory, and they elucidate a fundamental component of working memory span tasks.     

Decay and interference effects in motor short-term memory

Trace decay and interference effects in motor short-term memory were investigated by contrasting the predictions of two recent models (Pepper and Herman 1970; Laabs 1973) in regard to these two variables. Laabs' prediction that forgetting in motor short-term memory is indexed by greater variability of reproduction was supported in that movement reproduction after a 20 sec retention interval, either filled or unfilled, produced greater variable error. Further, his model was again supported in that analysis of constant error over five movement extents indicated interference effects through formation of an adaptation level which caused short movements to be overshot and long movements to be undershot. Pepper and Herman's concept of spontaneous trace decay indexed by a negative shift in constant error was not supported as was their prediction that interpolated activity would alter the strength of the criterion trace through an assimilation process. Finally, some evidence was found supporting the view that a memory trace can be strengthened through proprioceptive feedback entering through an unattended channel.     

Encoding strategy and retroactive interference in short-term memory

Abstract.— The effect of encoding strategy upon retroactive interference in STM was studied. The subjects were presented two trigrams for retention with the Brown-Peterson method. In half the cases they were to recall both trigrams, in half to recall only the first. The results showed higher recall with the associative than with the rehearsal strategy. An increase in level of retroactive interference was found to increase number of retroactive interference errors in the rehearsal strategy condition and number of omissions in the associative strategy condition. The results were interpreted in terms of the memory trace integration hypothesis.     

Reproduction and recognition in short-term visual memory

Reproduction and recognition in short-term visual memory was tested. In Experiment I, it was confirmed that the ability to reproduce visual figures in STM correlated with the ability to describe them. No such correlation was obtained when recall was by recognition. In Experiments II and III the mechanisms involved in the two types of recall were investigated by varying the character of the task interpolated in the retention interval. Results support the view that reproduction has a verbal component which is lacking in recognition.     

Time manages interference in visual short-term memory

Emerging evidence suggests that age-related declines in memory may reflect a failure in pattern separation, a process that is believed to reduce the encoding overlap between similar stimulus representations during memory encoding. Indeed, behavioural pattern separation may be indexed by a visual continuous recognition task in which items are presented in sequence and observers report for each whether it is novel, previously viewed (old), or whether it shares features with a previously viewed item (similar). In comparison to young adults, older adults show a decreased pattern separation when the number of items between “old” and “similar” items is increased. Yet the mechanisms of forgetting underpinning this type of recognition task are yet to be explored in a cognitively homogenous group, with careful control over the parameters of the task, including elapsing time (a critical variable in models of forgetting). By extending the inter-item intervals, number of intervening items and overall decay interval, we observed in a young adult sample (N?=?35, M_age?=?19.56 years) that the critical factor governing performance was inter-item interval. We argue that tasks using behavioural continuous recognition to index pattern separation in immediate memory will benefit from generous inter-item spacing, offering protection from inter-item interference.