Interference with Rehearsal in Spatial Working Memory in the Absence of Eye Movements

We have previously argued that rehearsal in spatial working memory is interfered with by spatial attention shifts rather than simply by movements to locations in space (Smyth & Scholey, 1994). It is possible, however, that the stimuli intended to induce attention shifts in our experiments also induced eye movements and interfered either with an overt eye movement rehearsal strategy or with a covert one. In the first experiment reported here, subjects fixated while they maintained a sequence of spatial items in memory before recalling them in order. Fixation did not affect recall, but auditory spatial stimuli presented during the interval did decrease performance, and it was further decreased if the stimuli were categorized as coming from the right or the left. A second experiment investigated the effects of auditory spatial stimuli to which no response was ever required and found that these did not interfere with performance, indicating that it is the spatial salience of targets that leads to interference. This interference from spatial input in the absence of any overt movement of the eyes or limbs is interpreted in terms of shifts of spatial attention or spatial monitoring, which Morris (1989) has suggested affects spatial encoding and which our findings suggest also affects reactivation in rehearsal.     

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.     

Characteristics of spatial memory span: Is there an analogy to the word length effect, based on movement time?

In studies of verbal short-term memory it has been shown that the length of words to be remembered affects the size of memory span. This word-length effect is attributed to relationships between the rate of rehearsal of verbal material and the time it takes to speak the words being rehearsed. For spatial memory span there may also be an internal rehearsal system linked to overt responding, and if there is a strong analogy to be drawn between the verbal and spatial domains then movement time between spatial targets should predict the number of spatial locations that can be recalled. In the experiments reported here the time taken to move between spatial targets is varied by altering the size of targets and the distance between them. No difference between span performance on a nine-block spatial span task were found, either on immediate recall or on recall after an interval. When recall is of items from an array of 27, grouped in nine sets of three, with only one location in any set being presented on any trial, there is an effect of display size. This effect is consonant with the argument that movement time is related to spatial rehearsal, but other explanations are also possible. However, if recall in this task is scored over the nine sets rather than over the 27 items, then there is no difference between the displays. The results indicate that performance on the normal nine-block spatial-span task cannot be predicted by movement time.     

Working memory for ballet moves and spatial locations in professional ballet dancers

The aim of the present study was to investigate working memory for ballet moves in expert dancers. Experiment 1 showed that a concurrent spatial task did not interfere with the recall of a sequence of ballet moves when these were encoded alone without being associated with spatial locations. Experiment 2 showed that a concurrent motor task selectively interfered with the recall of ballet moves while neither a concurrent motor task nor a spatial task affected recall of the specific locations where each ballet move had to be performed. Experiment 3 showed that spatial interference affected recall of sequences of locations when these were encoded alone. Finally, in Experiment 4, a similarity effect for patterned ballet movements was shown. Taken together results show that spatial interference does not affect short‐term memory for ballet moves thus suggesting that working memory might contain a system for motor configurations. Copyright © 2009 John Wiley & Sons, Ltd.     

Working memory for movements

Movement to spatial targets that can, in principle, be carried out by more than one effector can be distinguished from movements that involve specific configurations of body parts. The experiments reported here investigate memory span for a series of hand configurations and memory span for a series of hand movements to spatial locations. Spans were produced normally, or in conditions in which a suppression task was carried out on the right or the left hand while the movements to be remembered were presented. All movements were recalled using the right hand. There were two suppression tasks. One involved repeatedly squeezing a tube and so changing the configuration of the hand, and the other involved tapping a repeated series of spatial targets. The spatial tapping task interfered with span for spatial locations when it was presented on either the right or the left hand but did not affect span for movement pattern. The movement suppression task interfered with memory for movement pattern when it was presented on either the right or the left hand, but did not interfere with span for spatial locations. It is concluded that memory for movement configurations involves different processes from those used in spatial tasks and that there may be a need for a subsystem of working memory that is specific for movement configuration.     

Brain injury and movement recall: Preselection, active-passive and interference effects

Stroke patients with unilateral lesions were compared with age-controls and students on their ability to reproduce a terminal location established kinesthetically by a previous movement. Conditions for the criterion movement differed over active/passive and preselected/constrained (experiment 1) and whether the retention interval between the criterion and recall movements involved mental rehearsal of the criterion movement or yes/no responding to a mental arithmetic task (experiment 2). Whereas students showed more accurate recall with little effect of criterion movement condition, patient groups showed a preselection effect, but only with active movements. A preferred hand advantage observed for the patient controls did not occur with stroke patients, and prevention of mental rehearsal during the retention interval disrupted recall more for the stroke patients. These findings are interpreted in terms of hemisphere-specific coding strategies whose relative use depends on the attentional demands of the task.     

Motor expertise modulates movement processing in working memory

A substantial amount of literature has demonstrated individuals' tendency to code verbally a series of movements for subsequent recall. However, the mechanisms underlying movement encoding remain unclear. In this paper, I argue that sensorimotor expertise influences the involvement of motor processes to store movements in working memory. Experts in motor activities and individuals with limited motor expertise were compared in three experimental conditions assessing movement recall: (a) without suppression task, (b) with verbal suppression, and (c) with motor suppression. Athletes outperformed controls in movement recall, but the suppression tasks affected the two groups differently. Verbal suppression affected controls more than athletes, whereas the effect was reversed with motor suppression. Together, these findings suggest that controls and athletes favor different mechanisms to encode movements, either based on verbal or on motor processes, providing further evidence for a tight relationship between sensorimotor and cognitive processes.     

When looking back to nothing goes back to nothing

Previous research showed that the eyes revisit the location in which the stimulus has been encoded when visual or verbal information is retrieved from memory. A recent study showed that this behavior still occurs 1 week after encoding, suggesting that visual, spatial and linguistic information is tightly associated with the oculomotor trace and stored as an integrated memory representation. However, it is yet unclear whether looking behavior simply remains stable between encoding and recall or whether it changes over time in a more fine-tuned manner. Here, we investigate the time course of looking behavior during recall in multiple sessions across 1 week. Participants encoded visual objects presented in one of the four locations on the computer screen. In five sessions during the week after encoding, they performed on a visual memory recall task. During retrieval, participants looked back to the encoding location, but only in the recall sessions within 1 day of encoding. We discuss different explanations for the temporal dynamics of looking behavior during recall, searching for the role of eye movements in memory.     

Impaired Visuospatial Short-Term Memory in Children with ADHD

Previous studies provide clear evidence that visuospatial memory performance in children with attention-deficit/hyperactivity disorder (ADHD) is significantly lower than in typically developing children. In the present study, we investigated a major cause of their low performance using a spatial span test. Possibly, inattention resulting from lack of motivation or interest causes their low performance so that they do not correctly encode targets to be remembered. On the other hand, a deficit in temporary maintenance per se may cause their low performance; that is, their inefficient use of rehearsal during a retention interval may lead to memory traces’ fast decay. Results in this study indicated that children with ADHD could sustain attention during the encoding phase. Furthermore, their performance at delayed recall was significantly lower than immediate recall, but delayed recall did not affect typically developing children's performance. These results provide evidence for the likelihood that a factor causing children with ADHD difficulty in temporarily maintaining visuospatial information is fast decay of memory traces as a result of inefficient use of rehearsal, not inattention in the encoding phase.     

Visual–spatial attention aids the maintenance of object representations in visual working memory

Theories have proposed that the maintenance of object representations in visual working memory is aided by a spatial rehearsal mechanism. In this study, we used two different approaches to test the hypothesis that overt and covert visual–spatial attention mechanisms contribute to the maintenance of object representations in visual working memory. First, we tracked observers’ eye movements while they remembered a variable number of objects during change-detection tasks. We observed that during the blank retention interval, participants spontaneously shifted gaze to the locations that the objects had occupied in the memory array. Next, we hypothesized that if attention mechanisms contribute to the maintenance of object representations, then drawing attention away from the object locations during the retention interval should impair object memory during these change-detection tasks. Supporting this prediction, we found that attending to the fixation point in anticipation of a brief probe stimulus during the retention interval reduced change-detection accuracy, even on the trials in which no probe occurred. These findings support models of working memory in which visual–spatial selection mechanisms contribute to the maintenance of object representations.     

Rehearsal in serial memory for visual-spatial information: Evidence from eye movements

It is well established that rote rehearsal plays a key role in serial memory for lists of verbal items. Although a great deal of research has informed us about the nature of verbal rehearsal, much less attention has been devoted to rehearsal in serial memory for visual-spatial information. By using the dot task—a visual-spatial analogue of the classical verbal serial recall task—with delayed recall, performance and eyetracking data were recorded in order to establish whether visual-spatial rehearsal could be evidenced by eye movement. The use of eye movement as a form of rehearsal is detectable (Experiment 1), and it seems to contribute to serial memory performance over and above rehearsal based on shifts of spatial attention (Experiments 1 and 2).     

Effects of environmental support on overt and covert visuospatial rehearsal

People can rehearse to-be-remembered locations either overtly, using eye movements, or covertly, using only shifts of spatial attention. The present study examined whether the effectiveness of these two strategies depends on environmental support for rehearsal. In Experiment 1, when environmental support (i.e., the array of possible locations) was present and participants could engage in overt rehearsal during retention intervals, longer intervals resulted in larger spans, whereas in Experiment 2, when support was present but participants could only engage in covert rehearsal, longer intervals resulted in smaller spans. When environmental support was absent, however, longer retention intervals resulted in smaller memory spans regardless of which rehearsal strategies were available. In Experiment 3, analyses of participants’ eye movements revealed that the presence of support increased participants’ fixations of to-be-remembered target locations more than fixations of non-targets, and that this was associated with better memory performance. Further, although the total time fixating targets increased, individual target fixations were actually briefer. Taken together, the present findings suggest that in the presence of environmental support, overt rehearsal is more effective than covert rehearsal at maintaining to-be-remembered locations in working memory, and that having more time for overt rehearsal can actually increase visuospatial memory spans.     

Encoding location and serial order in auditory working memory: evidence for separable processes

In this study, we investigated the interactions between temporal and spatial information in auditory working memory. In two experiments, participants were presented with sequences of sounds originating from different locations in space and were then asked to recall either their position or their serial order. In Experiment 1, attention during encoding was manipulated by contrasting 'pure' blocks (i.e., location-only or serial-order-only trials) to 'mixed' blocks (i.e., different percentages of spatial and serial-order trials). In Experiment 2, 'pure' blocks were contrasted to blocks in which spatial and serial-order trials were intermixed with a third task requiring a semantic categorization of sounds. Results from both experiments showed that, whereas serial-order recall is linearly affected by the simultaneous encoding of a concurrent feature, the recall of position is mostly unaffected by concurrent feature encoding. Contrastingly, overall performance level was lower for spatial recall than serial recall. We concluded that serial order and location of items appear to be independently encoded in auditory working memory. Serial order is easier to recall, but strongly affected by the processing of concurrent item dimensions, while item location is more difficult to recall, but relatively automatic, as shown by its strong resistance to interfering dimensions in encoding.     

Pointing movements both impair and improve visuospatial working memory depending on serial position

Two experiments investigated the effects of pointing movements on the item and order recall of random, horizontal, and vertical arrays consisting of 6 and 7 squares (Experiment 1) or 8 and 9 squares (Experiment 2). In the encoding phase, participants either viewed the items passively (passive-view condition) or pointed towards them (pointing condition). Then, after a brief interval, they were requested to recall the locations of the studied squares in the correct order of presentation. The critical result was that, for all types of arrays, the effects of the encoding condition varied as a function of serial position: for the initial and central positions accuracy was higher in the passive-view than in the pointing condition (confirming the standard inhibitory effect of pointing movements on visuospatial working memory), whereas the reverse pattern occurred in the final positions—showing a significant advantage of the pointing condition over the passive-view condition. Findings are interpreted as showing that pointing can have two simultaneous effects on the recall of spatial locations, a positive one due to the addition of a motor code and a negative one due to the attentional requirements of hand movements, with the net impact on serial recall depending on the amount of attention resources needed for the encoding of each position. Implications for the item-order hypothesis and the perceptual-gestural account of working memory are also discussed.     

Spatial span under translation: A study of reference frames

The nature of the reference frame used to remember location sequences in a computer-presented version of spatial span was investigated by moving the template (a rectangular frame enclosing nine target squares) across the screen during presentation and/or during recall. Movement of the display during presentation substantially impaired memory in comparison with a stationary display (Experiment 1). However, there was no effect of template movement during recall (Experiment 2). In Experiments 3 and 4, the template was moved through the same screen locations during presentation and recall. When the extrinsic, or screen location, of each position was repeated identically on each trial but the sequence on the template varied, learning was not facilitated (Experiment 3). When the template sequences were repeated across trials but extrinsic location varied, the sequences were rapidly learned (Experiment 4). In this version of spatial span, location sequences appear to be encoded in an intrinsic frame of reference that is based on the template. Movement of the template during encoding impairs this process, possibly because concurrent attention shifts prevent the encoding of locations. The results are discussed with respect to recent studies of positional encoding in which multiple reference frames were available.     

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.     

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.     

Differentiating between verbal and spatial encoding using eye-movement recordings

Visual information processing is guided by an active mechanism generating saccadic eye movements to salient stimuli. Here we investigate the specific contribution of saccades to memory encoding of verbal and spatial properties in a serial recall task. In the first experiment, participants moved their eyes freely without specific instruction. We demonstrate the existence of qualitative differences in eye-movement strategies during verbal and spatial memory encoding. While verbal memory encoding was characterized by shifting the gaze to the to-be-encoded stimuli, saccadic activity was suppressed during spatial encoding. In the second experiment, participants were required to suppress saccades by fixating centrally during encoding or to make precise saccades onto the memory items. Active suppression of saccades had no effect on memory performance, but tracking the upcoming stimuli decreased memory performance dramatically in both tasks, indicating a resource bottleneck between display-controlled saccadic control and memory encoding. We conclude that optimized encoding strategies for verbal and spatial features are underlying memory performance in serial recall, but such strategies work on an involuntary level only and do not support memory encoding when they are explicitly required by the task.     

Oculomotor control and the maintenance of spatially and temporally distributed events in visuo-spatial working memory

Previous studies have demonstrated that working memory for spatial location can be significantly disrupted by concurrent eye or limb movement (Baddeley, 1986; Smyth, Pearson, & Pendleton, 1988). Shifts in attention alone can also interfere with spatial span (Smyth & Scholey, 1994), even with no corresponding movement of the eyes or limbs (Smyth, 1996). What is not clear from these studies is how comparable is the magnitude of effect caused by different forms of spatial disrupter. Recently, it has been demonstrated that limb movements produce as much interference with spatial span as do reflexive saccades (Lawrence, Myerson, Oonk, & Abrams, 2001). In turn this has led to the hypothesis that all spatially directed movement can produce similar effects in visuo-spatial working memory. This paper reports the results of five experiments that have contrasted the effect of concurrent eye movement, limb movement, and covert attention shifts on participants' working memory for sequences of locations. All conditions involving concurrent eye movement produced significantly greater reduction in span than equivalent limb movement or covert attention shifts with eyes fixated. It is argued that these results demonstrate a crucial role for oculomotor control processes during the rehearsal of location-specific representations in working memory.