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.     

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.     

Interference with spatial working memory: An eye movement is more than a shift of attention

In the present experiments, we examined whether shifts of attention selectively interfere with the maintenance of both verbal and spatial information in working memory and whether the interference produced by eye movements is due to the attention shifts that accompany them. In Experiment 1, subjects performed either a spatial or a verbal working memory task, along with a secondary task requiring fixation or a secondary task requiring shifts of attention. The results indicated that attention shifts interfered with spatial, butnot with verbal, working memory, suggesting that the interference is specific to processes within the visuospatial sketchpad. In Experiment 2, subjects performed a primary spatial working memory task, along with a secondary task requiring fixation, an eye movement, or an attention shift executed in the absence of an eye movement. The results indicated that both eye movements and attention shifts interfered with spatial working memory. Eye movements interfered to a much greater extent than shifts of attention, however, suggesting that eye movements may contribute a unique source of interference, over and above the interference produced by the attention shifts that accompany them.     

Covert shifts of attention can account for the functional role of “eye movements to nothing”

When trying to remember verbal information from memory, people look at spatial locations that have been associated with visual stimuli during encoding, even when the visual stimuli are no longer present. It has been shown that such “eye movements to nothing” can influence retrieval performance for verbal information, but the mechanism underlying this functional relationship is unclear. More precisely, covert in comparison to overt shifts of attention could be sufficient to elicit the observed differences in retrieval performance. To test if covert shifts of attention explain the functional role of the looking-at-nothing phenomenon, we asked participants to remember verbal information that had been associated with a spatial location during an encoding phase. Additionally, during the retrieval phase, all participants solved an unrelated visual tracking task that appeared in either an associated (congruent) or an incongruent spatial location. Half the participants were instructed to look at the tracking task, half to shift their attention covertly (while keeping the eyes fixed). In two experiments, we found that memory retrieval depended on the location to which participants shifted their attention covertly. Thus, covert shifts of attention seem to be sufficient to cause differences in retrieval performance. The results extend the literature on the relationship between visuospatial attention, eye movements, and verbal memory retrieval and provide deep insights into the nature of the looking-at-nothing phenomenon.     

Skilled Motor Performance and Working Memory in Rowers: Body Patterns and Spatial Positions

Previous studies using unfamiliar laboratory tasks (e.g. Smyth & Pendleton, 1990) have shown that working memory for movements to targets external to the body (positional movements) is dissociable from working memory for movements made to recreate specific configurations of body parts (patterned movements). In Experiment 1 this dissociation is replicated using tasks that were adapted for use in Experiment 2. In Experiment 2 the timing of experienced rowers' performance of patterned and positional elements of the rowing stroke was selectively disrupted by concurrent performance of patterned and positional memory tasks, respectively. These results suggest that patterned and positional elements of well-practised everyday motor tasks, which involve a complex interaction of the two types of movement, are controlled separately and place dissociable demands on working memory.     

Eye movements and the integration of visual memory and visual perception

Because visual perception has temporal extent, temporally discontinuous input must be linked in memory. Recent research has suggested that this may be accomplished by integrating the active contents of visual short-term memory (VSTM) with subsequently perceived information. In the present experiments, we explored the relationship between VSTM consolidation and maintenance and eye movements, in order to discover how attention selects the information that is to be integrated. Specifically, we addressed whether stimuli needed to be overtly attended in order to be included in the memory representation or whether covert attention was sufficient. Results demonstrated that in static displays in which the to-be-integrated information was presented in the same spatial location, VSTM consolidation proceeded independently of the eyes, since subjects made few eye movements. In dynamic displays, however, in which the to-be-integrated information was presented in different spatial locations, eye movements were directly related to task performance. We conclude that these differences are related to different encoding strategies. In the static display case, VSTM was maintained in the same spatial location as that in which it was generated. This could apparently be accomplished with covert deployments of attention. In the dynamic case, however, VSTM was generated in a location that did not overlap with one of the to-be-integrated percepts. In order to "move" the memory trace, overt shifts of attention were required.     

Covert shifts of attention precede involuntary eye movements

There is considerable evidence that covert visual attention precedes voluntary eye movements to an intended location. What happens to covert attention when an involuntary saccadic eye movement is made? In agreement with other researchers, we found that attention and voluntary eye movements are tightly coupled in such a way that attention always shifts to the intended location before the eyes begin to move. However, we found that when an involuntary eye movement is made, attention first precedes the eyes to the unintended location and then switches to the intended location, with the eyes following this pattern a short time later. These results support the notion that attention and saccade programming are tightly coupled.     

Movement and working memory: Patterns and positions in space

Five experiments are reported in which subjects were asked to remember short, visually presented sequences of whole body movement patterns, words, and spatial positions. The items were recalled in order in a memory span paradigm. During presentation of the items to be remembered subjects simply watched, or they carried out a concurrent activity involving articulatory suppression, movement to external spatial targets, or body-related movement. When the movement patterns to be remembered were familiar to subjects, movement span was not disrupted by articulatory suppression or movement to spatial targets but was disrupted by body-related movement. This movement suppression task, however, did not interfere with performance on a spatial span task or on verbal span. It is concluded that the memory for patterns of limb movement differs from memory for movement to spatial targets and that accounts of visuo-spatial processes in working memory involve the latter type of movement.     

Inhibition of saccadic eye movements to locations in spatial working memory

Inhibition of return (IOR) refers to a bias against overt and covert attentional orienting toward previously attended locations. According to the reorienting hypothesis, IOR is generated when attention is withdrawn from the attended location and is prevented from “returning” to it. The present study investigated whether maintenance of attention at the cued location could affect the inhibition of oculomotor orienting to it. To preclude disengagement of attention, we asked participants to maintain the cued location in working memory. Maintenance of visuospatial information in memory has been shown to be accomplished through a sustained shift of spatial attention to a memorized location. Our results show that oculomotor IOR occurs at a particular location even when that location is kept in working memory (Experiment 1). Furthermore, we demonstrate that the mere act of maintenance of a location in working memory produces oculomotor inhibition similar to IOR (Experiments 2 and 3). We conclude that the oculomotor system is used for coding and maintaining locations in spatial working memory. In addition, we demonstrate that endogenous attention associated with maintenance of a location in working memory can be dissociated from the attention needed for execution of a saccadic eye movement.     

The effects of eye and limb movements on working memory

Three experiments examined the role of eye and limb movements in the maintenance of information in spatial working memory. In Experiment 1, reflexive saccades interfered with memory span for spatial locations but did not interfere with memory span for letters. In Experiment 2, three different types of eye movements (reflexive saccades, pro-saccades, and anti-saccades) interfered with working memory to the same extent. In all three cases, spatial working memory was much more affected than verbal working memory. The results of these two experiments suggest that eye movements interfere with spatial working memory primarily by disrupting processes localised in the visuospatial sketchpad. In Experiment 3, limb movements performed while maintaining fixation produced as much interference with spatial working memory as reflexive saccades. These results suggest that the interference produced by eye movements is not the result of their visual consequences. Rather, all spatially directed movements appear to have similar effects on visuospatial working memory.     

Pupillary correlates of covert shifts of attention during working memory maintenance

The pupillary light reflex (PLR) was used to track covert shifts of attention to items maintained in visual working memory (VWM). In three experiments, participants performed a change detection task in which rectangles appeared on either side of fixation and at test participants indicated if the cued rectangle changed its orientation. Prior to presentation or during the delay, participants were cued to the light or dark side of the screen. When cued to the light side, the pupil constricted, and when cued to the dark side, the pupil dilated, suggesting that the PLR tracked covert shifts of attention. Similar covert shifts of attention were seen when the target stimuli remained onscreen and during a blank delay period, suggesting similar effects for attention to perceptual stimuli and attention to stimuli maintained in VWM. Furthermore, similar effects were demonstrated when participants were pre-cued or retro-cued to the prioritized location, suggesting that shifts of covert attention can occur both before and after target presentation. These results are consistent with prior research, suggesting an important role of covert shifts of attention during VWM maintenance and that the PLR can be used to track these covert shifts of attention.     

Neural dynamics of object-based multifocal visual spatial attention and priming: object cueing, useful-field-of-view, and crowding

How are spatial and object attention coordinated to achieve rapid object learning and recognition during eye movement search? How do prefrontal priming and parietal spatial mechanisms interact to determine the reaction time costs of intra-object attention shifts, inter-object attention shifts, and shifts between visible objects and covertly cued locations? What factors underlie individual differences in the timing and frequency of such attentional shifts? How do transient and sustained spatial attentional mechanisms work and interact? How can volition, mediated via the basal ganglia, influence the span of spatial attention? A neural model is developed of how spatial attention in the where cortical stream coordinates view-invariant object category learning in the what cortical stream under free viewing conditions. The model simulates psychological data about the dynamics of covert attention priming and switching requiring multifocal attention without eye movements. The model predicts how “attentional shrouds” are formed when surface representations in cortical area V4 resonate with spatial attention in posterior parietal cortex (PPC) and prefrontal cortex (PFC), while shrouds compete among themselves for dominance. Winning shrouds support invariant object category learning, and active surface-shroud resonances support conscious surface perception and recognition. Attentive competition between multiple objects and cues simulates reaction-time data from the two-object cueing paradigm. The relative strength of sustained surface-driven and fast-transient motion-driven spatial attention controls individual differences in reaction time for invalid cues. Competition between surface-driven attentional shrouds controls individual differences in detection rate of peripheral targets in useful-field-of-view tasks. The model proposes how the strength of competition can be mediated, though learning or momentary changes in volition, by the basal ganglia. A new explanation of crowding shows how the cortical magnification factor, among other variables, can cause multiple object surfaces to share a single surface-shroud resonance, thereby preventing recognition of the individual objects.     

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.     

Space and movement in working memory

Encoding seen movement of another human body requires visuo-spatial processing, and recall involves motor activity. However, encoding whole body movement patterns is affected differently by patterned and spatial secondary tasks, and this difference is reversed for encoding of spatial targets for movement (Smyth, Pearson, & Pendleton, 1988). The experiments reported here investigate the rehearsal of such movement patterns and their recall over unfilled and filled intervals. Performing, watching, or encoding a sequence of spatial positions while carrying a memory load of movement patterns did not affect recall of those movements, whereas performing, watching, or encoding a further set of patterned movements reduced the number recalled from the original set. However, memory for a series of locations in space was not affected by watching patterned movements during the interval, and only order information was affected by watching movement to a series of spatial locations during the interval. The results are discussed in terms of the independence of rehearsal mechanisms for spatial sequencing and movement patterns.     

FACILITATION OF SACCADES TOWARD A COVERTLY ATTENDED LOCATION IN EARLY INFANCY

Abstract— Covert shifts of visual attention may be demonstrated in both adult and infant subjects by facilitation of reaction times to make a saccade to a previously cued location However, this facilitation may be interpreted m terms of a direct effect on the eye movement system in the present experiment, we attempted to train 4-month-old infants to make a saccade in the location opposite from that in which a cue appeared Following such training, we examined the reaction lime to occasional probe targets that appeared in the same location as the cue Infants were faster to respond to a target in this location than they were to respond to it either in the training (expected) location or in baseline trials We interpret the results as providing further evidence for covert shifts of attention m 4-month-old infants, and suggest that the effects of covert shifts of attention on the eye movement system are independent of those from sequence learning     

Movement planning and attentional control of visuospatial working memory: evidence from a grasp-to-place task

In this study, we have investigated the influence of available attentional resources on the dual-task costs of implementing a new action plan and the influence of movement planning on the transfer of information into visuospatial working memory. To approach these two questions, we have used a motor–memory dual-task design in which participants grasped a sphere and planned a placing movement toward a left or right target according to a directional arrow. Subsequently, they encoded a centrally presented memory stimulus (4 × 4 symbol matrix). While maintaining the information in working memory, a visual stay/change cue (presented on the left, center or right) either confirmed or reversed the planned movement direction. That is, participants had to execute either the prepared or the re-planned movement and finally reported the symbols at leisure. The results show that both, shifts of spatial attention required to process the incongruent stay/change cues and movement re-planning, constitute processing bottlenecks as they both reduced visuospatial working memory performance. Importantly, the spatial attention shifts and movement re-planning appeared to be independent of each other. Further, we found that the initial preparation of the placing movement influenced the report pattern of the central working memory stimulus. Preparing a leftward movement resulted in better memory performance for the left stimulus side, while the preparation of a rightward movement resulted in better memory performance for the right stimulus side. Hence, movement planning influenced the transfer of information into the capacity-limited working memory store. Therefore, our results suggest complex interactions in that the processes involved in movement planning, spatial attention and visuospatial working memory are functionally correlated but not linked in a mandatory fashion.     

Value-driven attentional and oculomotor capture during goal-directed, unconstrained viewing

Covert shifts of attention precede and direct overt eye movements to stimuli that are task relevant or physically salient. A growing body of evidence suggests that the learned value of perceptual stimuli strongly influences their attentional priority. For example, previously rewarded but otherwise irrelevant and inconspicuous stimuli capture covert attention involuntarily. It is unknown, however, whether stimuli also draw eye movements involuntarily as a consequence of their reward history. Here, we show that previously rewarded but currently task-irrelevant stimuli capture both attention and the eyes. Value-driven oculomotor capture was observed during unconstrained viewing, when neither eye movements nor fixations were required, and was strongly related to individual differences in visual working memory capacity. The appearance of a reward-associated stimulus came to evoke pupil dilation over the course of training, which provides physiological evidence that the stimuli that elicit value-driven capture come to serve as reward-predictive cues. These findings reveal a close coupling of value-driven attentional capture and eye movements that has broad implications for theories of attention and reward learning.     

Remembering a location makes the eyes curve away

Working memory is a system that keeps limited information on-line for immediate access by cognitive processes. This type of active maintenance is important for everyday life activities. The present study shows that maintaining a location in spatial working memory affects the trajectories of saccadic eye movements toward visual targets, as the eyes deviate away from the remembered location. This finding provides direct evidence for a strong overlap between spatial working memory and the eye movement system. We argue that curvature is the result of the need to inhibit memory-based eye movement activity in the superior colliculus, in order to allow an accurate saccade to the visual target. Whereas previous research has shown that the eyes may deviate away from visually presented stimuli that need to be ignored, we show that the eyes also curve away from remembered stimuli.     

Covert shifts of attention function as an implicit aid to insight

Previous research shows that directed actions can unconsciously influence higher-order cognitive processing, helping learners to retain knowledge and guiding problem solvers to useful insights (e.g. Cook, S. W., Mitchell, Z., & Goldin-Meadow, S. (2008). Gesturing makes learning last. Cognition, 106, 1047-1058; Thomas, L. E., & Lleras, A. (2007). Moving eyes and moving thought: on the spatial compatibility between eye movements and cognition. Psychonomic Bulletin and Review, 14, 663-668). We examined whether overt physical movement is necessary for these embodied effects on cognition, or whether covert shifts of attention are sufficient to influence cognition. We asked participants to try to solve Duncker’s radiation problem while occasionally directing them, via an unrelated digit-tracking task, to shift their attention (while keeping their eyes fixed) in a pattern related to the problem’s solution, to move their eyes in this pattern, or to keep their eyes and their attention fixed in the center of the display. Although they reported being unaware of any relationship between the digit-tracking task and the radiation problem, participants in both the eye-movement and attention-shift groups were more likely to solve the problem than were participants who maintained fixation. Our results show that by shifting attention in a pattern compatible with a problem’s solution, we can aid participants’ insight even in the absence of overt physical movements.     

Spatial working memory and inhibition of return

Recently we showed that maintaining a location in spatial working memory affects saccadic eye movement trajectories, in that the eyes deviate away from the remembered location (Theeuwes, Olivers, & Chizk, 2005). Such saccade deviations are assumed to be the result of inhibitory processes within the oculomotor system. The present study investigated whether this inhibition is related to the phenomenon of inhibition of return (IOR), the relatively slow selection of previously attended locations as compared with new locations. The results show that the size of IOR to a location was not affected by whether or not the location was kept in working memory, but the size of the saccade trajectory deviation was affected. We conclude that inhibiting working memory-related eye movement activity is not the same as inhibiting a previously attended location in space.