On the locus of the stimulus suffix effect

Two experiments contrasted short-term memory and sensory memory (precategorical acoustic storage) explanations of the stimulus suffix effect. Experiment 1 attempted to interfere with recency recall by forcing subjects to encode nonverbal acoustic suffixes into a verbal, articulatory code. Subjects in this condition showed recall that was comparable to that of subjects who were told to ignore the suffixes. However, Experiment 2 showed that silently mouthed articulation of a suffix can produce interference on recall of recency items, although not as much as that produced by vocal articulation. The results are discussed in terms of current models of the stimulus suffix effect.     

Implicit and explicit memory for visual patterns

The article reports an investigation of implicit and explicit memory for novel, visual patterns. Implicit memory was assessed by a speeded perception task, and explicit memory by a four-alternative, forced-choice recognition task. Tests were given either immediately after testing or 7 days later. The results suggest that a single exposure of a novel, nonverbal stimulus is sufficient to establish a representation in memory that is capable of supporting long-lived perceptual priming. In contrast, recognition memory showed significant loss over the same delay. Performance measures in the two tasks showed stochastic independence on the first trial after a single exposure to each pattern. Finally, a specific occurrence of a previously studied item could be retrieved from explicit memory but did not affect the accuracy of perception in the implicit memory test. The results extend the domain of experimental dissociations between explicit and implicit memory to include novel, nonverbal stimuli.     

Serial position effects in 2-alternative forced choice recognition: Functional equivalence across visual and auditory modalities

Two experiments examined Ward, Avons, and Melling's (2005) proposition that the serial position function is task, rather than modality, dependent. Specifically, they proposed that for backward testing the 2-alternative forced-choice (2AFC) recognition paradigm is characterised by single-item recency irrespective of the modality of the stimulus presentation. In Experiment 1 the same nonword sequences, presented both visually or auditorily, produced qualitatively equivalent serial position functions with 2AFC testing. Forward testing produced a flat serial position function, while backward testing produced two-item recency in the absence of primacy. In order to rule out the possibility that the serial position functions for visual stimuli were the product of sub-vocal rehearsal, Experiment 2 employed articulatory suppression during the presentation phase. Serial position function equivalence was again observed together with a modest impairment in overall recognition rates. Taken together, these data are consistent with the Ward et al. proposition and further support the existence of a visual memory that can facilitate storage of visual-verbal material (e.g. Logie, Della Sella, Wynn, & Baddeley, 2000). However, the observation of two-item recency contradicts the original duplex account of single-item recency traditionally observed for backwards recognition testing of visual stimuli (Phillips & Christie, 1977).     

Temporal characteristics of visual memory

In order to infer the temporal relations among iconic, short-term, and long-term components of visual memory, random dot patterns were used as memory stimuli in six recognition memory experiments. Experiment 1 demonstrated that recognition was still above chance for intervals up to 12 s. In Experiments 2 and 3, an intervening masking stimulus was found to be effective only if presented within the first 500 ms of the interval. The remaining three experiments employed a two-target task, with the second target replacing the masking stimulus. Recognition performance with the second target was the same as that in a single-target task, whereas performance with the first target was almost at chance level. Increasing the interval between the targets resulted in a gradual improvement in the recognition of the first target.     

The effect of vowel similarity and syllable length on acoustic memory

Darwin and Baddeley (1974) argue that the presence of recency, suffix, and modality effects are not attributable to the acoustic properties of the stimuli but, rather, to the acoustic distance between the items comprising the test series. The present study is designed to determine whether stimulus duration is a significant variable in acoustic memory. Eight different blocks of synthetic stimuli were prepared; one block each of 60 msec similar and dissimilar syllables and 190 msec similar and dissimilar syllables. The other four blocks consisted of these same vocabularies, but each list in the block had an eighth syllable suffix of the same duration as the syllables in the block. Significant recency and suffix effects are seen for dissimilar syllables of both durations. No effects are demonstrated for 60-msec similar syllables, but both of the effects are seen for 190-msec similar syllables. These results indicate that whether or not a speech sound is preserved in precategorical acoustic storage (PAS) depends upon not only the acoustic distance between the stimuli, but also on other characteristics intrinsic to the stimuli, e.g., stimulus duration.     

Speed-accuracy tradeoff and information processing dynamics

For a long time, it has been known that one can tradeoff accuracy for speed in (presumably) any task. The range over which one can obtain substantial speed-accuracy tradeoff varies from 150 msec in some very simple perceptual tasks to 1,000 msec in some recognition memory tasks and presumably even longer in more complex cognitive tasks. Obtaining an entire speed-accuracy tradeoff function provides much greater knowledge concerning information processing dynamics than is obtained by a reaction- time experiment, which yields the equivalent of a single point on this function. For this and other reasons, speed-accuracy tradeoff studies are often preferable to reaction-time studies of the dynamics of perceptual, memory, and cognitive processes. Methods of obtaining speed-accuracy tradeoff functions include: instructions, payoffs, deadlines, bands, response signals (with blocked and mixed designs), and partitioning of reaction time. A combination of the mixed-design signal method supplemented by partitioning of reaction times appears to be the optimal method.     

Apparent shift in visual field preference after unilateral stroke

Patients with either a left- or a right-hemisphere stroke lesion scored higher in tasks of word-picture matching and of nonverbal shape matching when information was presented tachistoscopically (120 msec) to the visual field (VF) projecting to their undamaged hemisphere. Left-hemisphere stroke patients (n = 13) were dissociated from right-hemisphere stroke patients (n = 15) by low word recognition from memory and by low right VF but nearly normal left VF accuracy in word-picture matching or shape matching; the former appeared to rely upon processing of word meaning by the right hemisphere. In contrast, right-stroke patients had higher right than left VF scores in both tasks, and their discrimination of nonverbal shapes via the right VF was not different from that of controls (n = 15). Preferred processing by the VF projecting to the undamaged hemisphere appeared as a shift in perceptual asymmetry but may indicate, in support of a "direct access" model, that each hemisphere responds more or less efficiently to word and to nonverbal shape discriminations.     

Acquisition of information from rapidly presented verbal and nonverbal stimuli

Two experiments tested recognition memory for rapidly presented stimuli. In Experiment I 16 words were presented at exposure times ranging from 25 to 500 msec followed by a yes-no recognition test. The results showed a strong dependence of memory performance on both exposure time and serial position. In Experiment II 16 random forms were presented at exposure times ranging from 125 to 2000 msec followed by a yes-no recognition test. Results for random forms showed that memory performance was strongly dependent on exposure time but not on serial position. Taken together, the results of Experiments I and II suggest qualitative encoding differences between verbal vs nonverbal stimuli.     

Task difficulty and visual similarity increase a distractor's effects on random shapes

Recognition of random shapes followed by a visual distractor is altered by the type of distractor and whether the distractor needs to be attended. Three experiments tested which characteristics modify a visual distractor's effect on random target shapes presented for 75 to 150 msec. Exp. 1 showed that increasing the number of digits to be remembered (1, 3, or 8) increased the effectiveness of digits as distractors. Exeir effect as visual distractors for random target shapes. Random shapes were highly effective as distractors, while pictures of faces or comples colored pictures had a relatively small effect. In Exp. 3 decreasing the presentation time for novel visual distractors decreased recognition of the distractors but not of random target shapes. However, adding a three-digit distractor after the novel visual distractor did decrease recognition of target shapes. Exps. 2 and 3 showed that the order of the recognition tests of the target and distracting stimuli altered target recognition if and only if subjects did know which was to be reported first. These experiments indicate that the effect of a visual distractor depends on both the extent to which it is allotted attention and its visual similarity to the target stimulus.     

Effect of display movement on tactile pattern perception

The effect of display movement on the ability of subjects to rec ognize alphabetic shapes tactually was investigated. The display consisted of a computer-controlled 8-by-6 array of small airjet stimulators that could be physically translated in a small circle by means of a mechanical linkage. The experimental parameters were the stimulus duration, the angular velocity of the display, and the amplitude of the rotation. Recognition accuracy increased with stimulus duration between 100 and 400 msec. For a rotation amplitude of 0.8 cm, a maximum in recognition accuracy occurred at a rotation velocity of 400 rpm, or 150 msec. per revolution. The optimum angular velocity appeared to decrease as the amplitude of rotation increased. From these results and certain related neurophysiological evidence, a hypothetical model is suggested which qualitatively can account for the data.     

Effect of display movement on tactile pattern perception

The effect of display movement on the ability of subjects to recognize alphabetic shapes tactually was investigated. The display consisted of a computer-controlled 8-by-6 array of small airjet stimulators that could be physically translated in a small circle by means of a mechanical linkage. The experimental parameters were the stimulus duration, the angular velocity of the display, and the amplitude of the rotation. Recognition accuracy increased with stimulus duration between 100 and 400 msec. For a rotation amplitude of 0.8 cm, a maximum in recognition accuracy occurred at a rotation velocity of 400 rpm, or 150 msec. per revolution. The optimum angular velocity appeared to decrease as the amplitude of rotation increased. From these results and certain related neurophysiological evidence, a hypothetical model is suggested which qualitatively can account for the data.     

Direct measures of short-term visual storage

Two experiments, involving seven conditions, explored the use of direct measures of visual persistence. In each, the subject was asked to judge if an intermittent stimulus appeared perceptually continuous, or whether it completely faded before the next presentation occurred. The first experiment showed that visual persistence was set at approximately 250 msec. for a recycling presentation of a circle in a tachistoscope; in another task employing a moving opaque slit passing back and forth over a circle, persistence times averaged 50 msec. longer. Reducing luminance by 2 log units increased persistence only slightly, though removing the adapting field increased it by over 100 msec. The second experiment, using the repeating circle, varied the duration of the stimulus, and compared monoptic with dichoptic presentations. Visual persistence was found to be independent of stimulus duration over a range of 4 to 200 msec., where all durations were above recognition threshold for the stimulus. Persistence was unaffected whether the stimulus was repeatedly presented in the same eye or alternated between eyes, strongly suggesting that the storage is central. Finally, a re-analysis of Dodwell and Engel's paper on stereopsis suggests that their effects can be adequately explained by visual persistence of the asynchronous stereo pairs, rather than a more complex fusion model. All of these results strongly support the use of visual persistence as a direct measure of short-term visual storage.     

Recognition Memory in Pigeons for Stimuli Presented Repeatedly: Perceptual Learning or Reduced Associative Interference?

Todd and Mackintosh (1990) found that recognition memory of pigeons for pictures was better when the same pictures were used each session (a recency task) than when different slides were used (a novelty task); they attributed the superior performance on the recency task to perceptual learning. Three experiments explored two alternative accounts. One was that their use of a within-subject design could have allowed the strategy adopted in the recency task to influence adversely the strategy used in the novelty task. This possibility was ruled out by Experiment 1, which showed superior performance in the recency task when a between-subject design was used. A second account proposes that slide-reward associations formed (in both tasks) during first presentations of slides interfere with appropriate performance during second presentations (associative interference); in the recency task, however, the high long-term associative strength of the slides restricts the consequence of a single slide-reward pairing to a short-term effect, and associative interference occurs at short retention intervals only. This account was explored in Experiment 2, which found no evidence that increases in retention interval resulted in reduction of associative interference in the recency task, and in Experiment 3, where associative interference was shown to occur but was of comparable magnitude in the recency and novelty tasks. By elimination, the results support a perceptual learning interpretation.     

Dissociation of short- and long-term face memory: evidence from long-term recency effects in temporal lobe epilepsy

We tested whether memory deficits in temporal lobe epilepsy (TLE) are better described by a single- or dual-store memory model. To this aim, we analyzed the influence of TLE and proactive interference (PI) on immediate and 24-h long-term recency effects during face recognition in 16 healthy participants and 18 right and 21 left non-surgical TLE patients. PI in healthy participants or TLE erased the long-term recency effect, but left the immediate recency effect unaffected. Although the immediate recency effect was still visible in right TLE patients, the number of detected recency items during immediate recognition was decreased in right TLE compared to left TLE. Right TLE was also related to decreased detection of pre-recency items during delayed recognition compared to left TLE, and decreased detection of pre-recency items during immediate recognition under PI. The results show that the temporal lobes are necessary for the long-term recency effect, but not for the immediate recency effect, and thus speak for a dissociation of short- and long-term memory for faces. Right TLE is related to more severe long-term memory deficits than left TLE and is also related to additional short-term memory deficits for faces.     

Working and long-term memory deficits in schizophrenia: is there a common prefrontal mechanism?

This study tested the hypothesis that dorsolateral prefrontal cortex deficits contribute to both working memory and long-term memory disturbances in schizophrenia. It also examined whether such deficits were more severe for verbal than nonverbal stimuli. Functional magnetic resonance imaging was used to assess cortical activation during performance of verbal and nonverbal versions of a working memory task and both encoding and recognition tasks in 38 individuals with schizophrenia and 48 healthy controls. Performance of both working memory and long-term memory tasks revealed disturbed dorsolateral prefrontal cortex activation in schizophrenia, although medial temporal deficits were also present. Some evidence was found for more severe cognitive and functional deficits with verbal than nonverbal stimuli, although these results were mixed.     

Two types of short-term visual storage

Seven-letter words were flashed repetitively at various durations above and below the recognition threshold for single flashes. One form of a short-term storage effect was studied by measuring the interstimulus interval between flashes at which S reported that the stimulus became phenomenally discontinuous in time. Storage times reached a maximum of about 300 msec in this task. A second form of storage effect was measured by decreasing the interstimulus interval until S could correctly recognize a repeated stimulus whose duration was below the single-flash recognition threshold; this effect extended to 900 msec in some cases. Each of these effects was reliably obtained for both rare and frequent words. Both forms of storage were increased by providing a dark rather than a lighted adapting field between presentations of the test stimulus. Implications for Information processing of brief displays are discussed.     

Eye movements serialize memory for objects in scenes

A gaze-contingent short-term memory paradigm was used to obtain forgetting functions for realistic objects in scenes. Experiment 1 had observers freely view nine-item scenes. After observers' gaze left a predetermined target, they could fixate from 1-7 intervening nontargets before the scene was replaced by a spatial probe at the target location. The task was then to select the target from four alternatives. A steep recency benefit was found over the 1-2 intervening object range that declined into an above-chance prerecency asymptote over the remainder of the forgetting function. In Experiment 2, we used sequential presentation and variable delays to explore the contributions of decay and extrafoveal processes to these behaviors. We conclude that memory for objects in scenes, when serialized by fixation sequence, shows recency and prerecency effects that are similar to isolated objects presented sequentially over time. We discuss these patterns in the context of the serial order memory literature and object file theory.     

Recency effect in recall of a word list when an immediate memory task is performed after each word presentation

Subjects studied 12-word lists for free recall. During presentation of the lists, each word was followed by a supraspan sequence of digits, which the subjects tried to reproduce. This task, unlike those used in previous research with this continual distractor procedure, presumably taxed immediate memory capacity to the full. Nevertheless, the word recall data showed a pronounced recency effect. Moreover, the magnitude of the recency effect was found to be just as great with this task as with a more typical task in which the demands on immediate memory are likely to be fewer. These findings reinforce the emerging view that the recency effect need not be the product of immediate memory.     

Visual memory and stimulus repetition effects

Recent investigations of memory for randomly configured patterns indicate that visual memory can involve distinct short-term and long-term components. The appearance of a visual recency effect that is confined to the last-presented item is believed to result from the active visualization of this item during the retention interval. Studies of the retention of familiar visual information have also suggested that the short-term effects observed are a result of active visualization. In a review of these studies, however, we argue that the effects obtained with familiar visual information are not necessarily a result of active visualization and, indeed, may not involve anything other than long-term visual memory. For example, Rabbitt and Vyas (1979) observed a visual recency effect in a serial choice reaction time task involving familiar information. That this recency effect was confined to the final item accords with the results obtained with unfamiliar visual information. However, this choice reaction time task did not require subjects to remember previous stimuli, so it is unlikely that they actively visualized them. With the case for a distinct short-term visual memory currently resting on the recency effect interpreted as reflecting a process of active visualization, this result is especially important. In the second part of the present paper, we report a series of experiments that provides an understanding of the visual recency effect in the serial choice reaction time task. We conclude from these studies that this effect is not due to visualization or to a visual trace either decaying or being overwritten by a succeeding stimulus.