Reactivation-induced interference in a short-term retention paradigm

In Experiment 1 it was demonstrated that interference with a rat's retention of a target spatial cue decreases as the interval between prior conflicting cues and the target increases. Experiment 2 showed that interference can occur even when the interstimulus interval is long, if the memory of a conflicting cue is reactivated just prior to exposing an animal to the target cue. A third experiment suggested that these findings could not be easily interpreted in terms of a stimulus satiation effect. The implications of these findings for a trace decay model of short-term retention were discussed.     

Reminder-induced recovery from blocking as a function of the number of compound trials

Conditioned lick suppression in rats was employed to examine changes in the associative status of a blocked stimulus as a function of the number of compound stimulus conditioning trials. In each of two experiments, prior tone-footshock pairings produced similar blocking of conditioned responding to the light element of a tone-light compound when either two or six compound trials were used. In experiment 1, two exposures to the light alone in a dissimilar context during the retention interval, i.e., a reminder treatment, resulted in a restoration of responding to the light which was complete and similar for animals receiving two or six compound trials. This indicated that latent acquisition with respect to the blocked stimulus was largely complete after two compound trials. Because of a potential ceiling effect for reminder-induced recovery from blocking, Experiment 2 employed an attenuated reminder (one light exposure). This reminder reversed the blocking when six, but not when two, compound trials were used. These results suggest that, after latent acquisition to the blocked stimulus is complete, the blocked stimulus continues to be processed during additional compound stimulus conditioning trials, with a consequent latent facilitation of retrieval of associations to the blocked stimulus.     

Alleviating forgetting of active shock-avoidance by apparently unrelated food presentations

A series of four experiments investigated why forgetting of an active shock-avoidance response was reduced when an apparently unrelated appetitive experience occurred both prior to avoidance training and during the retention interval between training and testing. Experiments 1 and 2 demonstrated the reliability of the phenomenon and found that a sufficient condition for the effect was the presentation of food from a pellet dispenser (not an operant response per se). Experiment 3 demonstrated that the effect was not the result of enhanced activity. Experiment 4 showed that forgetting was still reduced when the appetitive experience occurred only prior to active avoidance or only during the retention interval. The results are discussed in regard to the reinstatement of the reinforcer representation.     

Inhibitory interaction: the effects of multiple non-predictive visual cues

When the interval between a non-predictive cue and a target appearing at the same spatial location is longer than about 200 ms, target performance is typically poorer than when the cue and target appear at different locations. Recent studies have shown that this effect, known as inhibition of return (IOR), can occur at multiple cued locations, and is enhanced when multiple cues are presented at the same spatial location. However, little is known about how the magnitude of IOR at one spatial location is influenced by a subsequent or preceding cue presented at a different spatial location. We investigated this issue by presenting single or multiple cues at varying inter-cue intervals prior to target onset. Results suggest that the magnitude of IOR at a given location is influenced by the presentation of a preceding cue, but that once IOR occurs, it is unaffected by the presentation of a subsequent cue.     

Visual working memory load disrupts the space‐based attentional guidance of target selection

During visual search, the selection of target objects is guided by stored representations of target‐defining features (attentional templates). It is commonly believed that such templates are maintained in visual working memory (WM), but empirical evidence for this assumption remains inconclusive. Here, we tested whether retaining non‐spatial object features (shapes) in WM interferes with attentional target selection processes in a concurrent search task that required spatial templates for target locations. Participants memorized one shape (low WM load) or four shapes (high WM load) in a sample display during a retention period. On some trials, they matched them to a subsequent memory test display. On other trials, a search display including two lateral bars in the upper or lower visual field was presented instead, and participants reported the orientation of target bars that were defined by their location (e.g., upper left or lower right). To assess the efficiency of attentional control under low and high WM load, EEG was recorded and the N2pc was measured as a marker of attentional target selection. Target N2pc components were strongly delayed when concurrent WM load was high, indicating that holding multiple object shapes in WM competes with the simultaneous retention of spatial attentional templates for target locations. These observations provide new electrophysiological evidence that such templates are maintained in WM, and also challenge suggestions that spatial and non‐spatial contents are represented in separate independent visual WM stores.     

Overt is no better than covert when rehearsing visuo-spatial information in working memory

In the present study, we examined whether eye movements facilitate retention of visuo-spatial information in working memory. In two experiments, participants memorised the sequence of the spatial locations of six digits across a retention interval. In some conditions, participants were free to move their eyes during the retention interval, but in others they either were required to remain fixated or were instructed to move their eyes exclusively to a selection of the memorised locations. Memory performance was no better when participants were free to move their eyes during the memory interval than when they fixated a single location. Furthermore, the results demonstrated a primacy effect in the eye movement behaviour that corresponded with the memory performance. We conclude that overt eye movements do not provide a benefit over covert attention for rehearsing visuo-spatial information in working memory.     

Enhanced long-term and impaired short-term spatial memory in GluA1 AMPA receptor subunit knockout mice: Evidence for a dual-process memory model

The GluA1 AMPA receptor subunit is a key mediator of hippocampal synaptic plasticity and is especially important for a rapidly-induced, short-lasting form of potentiation. GluA1 gene deletion impairs hippocampus-dependent, spatial working memory, but spares hippocampus-dependent spatial reference memory. These findings may reflect the necessity of GluA1-dependent synaptic plasticity for short-term memory of recently visited places, but not for the ability to form long-term associations between a particular spatial location and an outcome. This hypothesis is in concordance with the theory that short-term and long-term memory depend on dissociable psychological processes. In this study we tested GluA1^−/− mice on both short-term and long-term spatial memory using a simple novelty preference task. Mice were given a series of repeated exposures to a particular spatial location (the arm of a Y-maze) before their preference for a novel spatial location (the unvisited arm of the maze) over the familiar spatial location was assessed. GluA1^−/− mice were impaired if the interval between the trials was short (1 min), but showed enhanced spatial memory if the interval between the trials was long (24 h). This enhancement was caused by the interval between the exposure trials rather than the interval prior to the test, thus demonstrating enhanced learning and not simply enhanced performance or expression of memory. This seemingly paradoxical enhancement of hippocampus-dependent spatial learning may be caused by GluA1 gene deletion reducing the detrimental effects of short-term memory on subsequent long-term learning. Thus, these results support a dual-process model of memory in which short-term and long-term memory are separate and sometimes competitive processes.     

Mapping the timecourse of goal-directed attention to location and colour in human vision

Goal-directed attention prioritises perception of task-relevant stimuli according to location, features, or onset time. In this study we compared the behavioural timecourse of goal-directed selection to locations and colours by varying the stimulus-onset asynchrony (SOA) between cue and target in a strategic cueing paradigm. Participants reported the presence or absence of a target following prior information regarding its location or colour. Results revealed that preparatory selection by colour is more effective at enhancing perceptual sensitivity than selection by location, even though both types of cue provided equivalent overall information. More detailed analysis revealed that this advantage arose due a limitation of spatial attention in maintaining a sufficiently broad focus (>2°) for target detection across multiple stimuli. In contrast, when target stimuli fell within 2° of the spatial attention spotlight, the strategic advantages and speed of spatial and colour attention were equated. Our findings are consistent with the conclusion that, under spatially optimal conditions, prior spatial and colour information are equally proficient at guiding top-down selection. When spatial locations are ambiguous, however, colour-based selection is the more efficient mechanism.     

Dissociating cognitive and motor interference effects on kinesthetic short-term memory

In two experiments, we investigated how short-term memory of kinesthetically defined spatial locations suffers from either motor or cognitive distraction. In Exp. 1, 22 blindfolded participants moved a handle with their right hand towards a mechanical stop and back to the start and then reproduced the encoded stop position by a second movement. The retention interval was adjusted to approximately 0 and 8 s. In half of the trials participants had to provide a verbal judgment of the target distance after encoding (cognitive distractor). Analyses of constant and variable errors indicated that the verbal judgments interfered with the motor reproduction only, when the retention interval was long. In Exp. 2, 22 other participants performed the same task but instead of providing verbal distance estimations they performed an additional movement either with their right or left hand during the retention interval. Constant error was affected by the side of the interpolated movement (right vs. left hand) and by the delay interval. The results show that reproduction of kinesthetically encoded spatial locations is affected differently in long- and short-retention intervals by cognitive and motor interference. This suggests that reproduction behavior is based on distinct codes during immediate vs. delayed recall.     

The time course of spatial memory distortions

Four experiments investigated the memory distortions for the location of a dot in relation to two horizontally aligned landmarks. In Experiment 1, participants reproduced from memory a dot location with respect to the two landmarks. Their performance showed a systematic pattern of distortion that was consistent across individual participants. The three subsequent experiments investigated the time course of spatial memory distortions. Using a visual discrimination task, we were able to map the emergence of spatial distortions within the first 800 msec of the retention interval. After retention intervals as brief as 50 msec, a distortion was already present. In all but one experiment, the distortion increased with longer retention intervals. This early onset of spatial memory distortions might reflect the almost immediate decay of detailed spatial information and the early influence of an enduring spatial memory representation, which encodes spatial information in terms of the perceived structure of space.     

Pigeons' spatial memory: III. Effect of distractors on delayed matching of key location.

The effect of distractors on pigeons' delayed matching of key location was investigated. Baseline trials began with a "ready" stimulus (brief operation of the grain feeder). Then one (randomly chosen) key from a three-by-three matrix was lit briefly as the sample. After a short delay (retention interval) the sample key was lit again along with one of the other eight keys. A peck at the key that had served as the sample (correct comparison) produced grain reinforcement, whereas a peck to the other key (incorrect comparison) produced only the intertrial interval. In Experiment 1, a houselight distractor, presented during either the sample, retention interval, or choice phases of the trial, had little if any effect on accuracy of matching key location. In Experiment 2, one of three types of spatial stimuli was interpolated during the retention interval, or the interval was blank as during baseline trials. The three stimuli were: the sample (correct comparison) location for that trial, the incorrect comparison location for that trial, or one of the seven unused locations for that trial. Relative to blank trials, accuracy improved slightly on sample-interpolated trials, decreased slightly on unused location-interpolated trials, and decreased considerably on incorrect comparison-interpolated trials. In Experiment 3, retention intervals were blank or had one of six types of interpolation: the sample, the incorrect comparison, two presentations of the sample, two presentations of the incorrect comparison, the sample followed by the incorrect comparison, or the incorrect comparison followed by the sample.(ABSTRACT TRUNCATED AT 250 WORDS)     

Parafoveal attention in congenitally deaf and hearing young adults

This reaction-time study compared the performance of 20 congenitally and profoundly deaf, and 20 hearing college students on a parafoveal stimulus detection task in which centrally presented prior cues varied in their informativeness about stimulus location. In one condition, subjects detected a parafoveally presented circle with no other information being present in the visual field. In another condition, spatially complex and task-irrelevant foveal information was present which the subjects were instructed to ignore. The results showed that although both deaf and hearing people utilized cues to direct attention to specific locations and had difficulty in ignoring foveal information, deaf people were more proficient in redirecting attention from one spatial location to another in the presence of irrelevant foveal information. These results suggest that differences exist in the development of attentional mechanisms in deaf and hearing people. Both groups showed an overall right visual-field advantage in stimulus detection which was attenuated when the irrelevant foveal information was present. These results suggest a left-hemisphere superiority for detection of parafoveally presented stimuli independent of cue informativeness for both groups.     

Cocktail party listening in a dynamic multitalker environment

A priori information about the location of the target talker plays a critical'role in cocktailparty listening tasks, but little is known about the influence of imperfect spatial information in situations in which the listener has some knowledge about the location of the target speech but does not know its exact location prior to hearing the stimulus. In this study, spatial uncertainty was varied by adjusting the probability that the target talker in a multitalker stimulus would change locations at the end of each trial. The results show that listeners can adapt their strategies according to the statistical properties of a dynamic acoustic environment but that this adaptation is a relatively slow process that may require dozens of trials to complete.     

Movement versus focusing of visual attention

In two experiments, we investigated the idea that attention moves through visual space in an analog fashion. The spatial distribution of attention was determined by presenting a spatially informative cue and comparing reaction times to targets at cued and uncued locations as a function of the interval from cue onset to target onset (SOA). Facilitation and inhibition were measured by reference to a neutral condition in which the cue provided no spatial information. In the first experiment, we used a central cue (an arrow), and in the second experiment, we used a peripheral cue (a 50-msec flash). With central cue, the facilitatory effects of the cuing were initially equal for all locations on the indicated side of the display, and then decreased for all locations except the one that had been specifically cued. These results are interpreted as being more consistent with "focusing" of an initially broad "beam" of attention than with "movement" of a narrow beam from fixation to the cued location. With peripheral cues, strong facilitation specific to the cued location was manifest as early as 50 msec after cue onset, but this effect decreased with increasing SOA. Inhibition for uncued locations increased with increasing SOA at a rate that generally reflected their distance from the cued location. Taken together, these results reveal important differences between peripheral and central cues in the generation of attentional selectivity, not just in the time-course of events, but also in the nature of the processes involved.     

Effects of sexual versus fear arousal on alcohol consumption in college males

To compare the effects of pleasant and aversive arousal on alcohol consumption, 18 male undergraduates had three weekly sessions to separately view erotic, mutilation or neutral slides in a simulated memory experiment. Following exposure to the slides, they received access to alcoholic and nonalcoholic beverages, which were presented to half the subjects in a taste rating task, and to half as the result of engaging in an operant lever-press task. Subjects believed these tasks to be distractors during a purported retention interval. Self-report instruments and basal skin conductance confirmed the success of the affective manipulations. However, only the subjects using the taste task after viewing erotic slides significantly increased alcohol consumption. These results question a tension reduction model of drinking and qualify the contribution of autonomic arousal to motivation for drinking.     

The impact of multiple irrelevant visual events at the same spatial location on inhibition

If an irrelevant visual event, such as a nonpredictive cue, is presented prior to a target, performance is impaired when the target appears at the cued location relative to when it is presented at an uncued location. This phenomenon, referred to as inhibition of return, can be found at multiple spatial locations when each is cued in succession. The present study examined the effect of successively cuing the same spatial location. Results suggested that additional inhibition occurred when more than one cue appeared at a single location at longer intercue intervals, but not at shorter intervals. These findings suggest that total inhibition to respond to targets at a spatial location reflects a summation of facilitatory and inhibitory factors generated by the presentation of each cue.     

Training attention: Interactions between central cues and reflexive attention

Three experiments are reported in which we investigate whether the recently reported interactions between central cues (e.g., arrows) and reflexive attention are attributable to the overlearned spatial properties of certain central cues. In all three experiments, a nonpredictive cue with arbitrary spatial properties (a colour patch) is presented prior to a detection target in the left or right visual field. Reaction times to detect targets are compared before and after a training session in which participants are trained to associate each colour patch with left and right space, either via a target detection task in which colour predicts target location 100% of the time (Experiments 1 and 3), or via a left/right motor movement as a function of colour (Experiments 2 and 3). In the first two experiments, a small but highly significant training effect is observed. Participants are approximately 10 ms faster to detect targets at congruent locations relative to incongruent locations after training relative to before training, despite the fact that cue colour was nonpredictive during the test sessions. In Experiment 3, the length of the training session is increased and the magnitude of the training effect also increases as a result. Implications for the interaction between central cues and reflexive attention, as well as premotor theory of attention, are discussed.     

The impact of path crossing on visuo-spatial serial memory: Encoding or rehearsal effect?

The determinants of visuo-spatial serial memory have been the object of little research, despite early evidence that not all sequences are equally remembered. Recently, empirical evidence was reported indicating that the complexity of the path formed by the to-be-remembered locations impacted on recall performance, defined for example by the presence of crossings in the path formed by successive locations (Parmentier, Elford, & Maybery, 2005). In this study, we examined whether this effect reflects rehearsal or encoding processes. We examined the effect of a retention interval and spatial interference on the ordered recall of spatial sequences with and without path crossings. Path crossings decreased recall performance, as did a retention interval. In line with the encoding hypothesis, but in contrast with the rehearsal hypothesis, the effect of crossing was not affected by the retention interval nor by tapping. The possible nature of the impact of path crossing on encoding mechanisms is discussed.     

The impact of path crossing on visuo-spatial serial memory: encoding or rehearsal effect?

The determinants of visuo-spatial serial memory have been the object of little research, despite early evidence that not all sequences are equally remembered. Recently, empirical evidence was reported indicating that the complexity of the path formed by the to-be-remembered locations impacted on recall performance, defined for example by the presence of crossings in the path formed by successive locations (Parmentier, Elford, & Maybery, 2005). In this study, we examined whether this effect reflects rehearsal or encoding processes. We examined the effect of a retention interval and spatial interference on the ordered recall of spatial sequences with and without path crossings. Path crossings decreased recall performance, as did a retention interval. In line with the encoding hypothesis, but in contrast with the rehearsal hypothesis, the effect of crossing was not affected by the retention interval nor by tapping. The possible nature of the impact of path crossing on encoding mechanisms is discussed.     

Components of the location probability effect in visual search tasks

In visual search tasks, targets are detected more rapidly when they appear in locations that commonly contain a target than when they appear in locations that rarely contain a target. Five experiments were conducted to investigate two specific properties of this location probability effect: its dependence on spatial location versus relative position and its dependence on or independence of target identity. In Experiment 1 spatial location of a stimulus row was varied to determine whether high location probability facilitates target detection in a particular location in visual space or a particular relative position within the row. Both were facilitated to approximately the same extent. In Experiment 2 an inducing target occurred with high probability in one of four display locations, and a test target occurred with equal probability in all four locations. Both targets were found more quickly in the high-probability location than in the other locations, but the advantage associated with targets in the high-probability location was larger for the inducing target than for the test target. In Experiments 3-5 the correspondence between the components observed in Experiments 1 and 2 was examined. The overall pattern of results was compatible with a model in which the location probability effect is produced partly by an attentional spotlight, which facilitates processing of any stimulus appearing in a particular location in visual space, and partly by a network of position-specific letter detectors, which facilitates detection of a particular letter in a particular relative position within a display. Models with flexible scanning strategies were also considered.