Short-term Memory For Spatial Locations Research Articles

Endogenous variation in estradiol in women affects the weighting of metric and categorical information in spatial location memory

Recent work has suggested that sex differences may exist in the strategies or types of cues that are utilized by men and women to remember discrete spatial locations or routes through a visual environment. The current study investigated the effects of circulating estradiol levels in women on the relative weighting of categorical versus fine-grained ‘metric’ information in a test of short-term memory for spatial locations, either presented within a simple geometric surround (a circular enclosure) or within more visually complex landscape scenes. Patterns of displacement error in the point location estimates made by men and women were analyzed. Results confirmed a sex difference in the weighting of metric versus categorical cues. Relative to men, women's estimates of locations were more strongly biased toward the center of the surrounding category (i.e., toward the category ‘prototype’). Furthermore, objective measures of estradiol via saliva collected at the time of memory testing showed that, among naturally-cycling women, estradiol concentrations correlated in a positive, graded, fashion with the degree of emphasis that women placed on categorical information when estimating point locations. No associations were found for progesterone. These findings are consistent with a wider body of research showing that biological sex and reproductive hormone levels, including 17β-estradiol, can subtly influence performance on certain spatial tasks. This is the first study to show that circulating estradiol levels may influence the relative emphasis placed on categorical versus metric cues when remembering simple point locations.

Rightward exogenous attentional shifts impair perceptual memory of spatial locations in patients with left unilateral spatial neglect

Spatial remapping implies the updating and maintaining of the spatial position of objects in successive visual images across time, despite their displacement on the retina due to eye movements. In the parietal cortex, the representation of spatial locations appears to be partly centered on gaze direction, and thus modulated by current eye-gaze position. It has been suggested that short-term memory for spatial locations across delays might be impaired in right brain-injured patients with left spatial neglect, but more so after rightward than leftward gaze shifts – an asymmetry attributed to a loss of spatial representations normally transferred from left to right hemisphere during remapping. Because several studies point to a strong link between attentional and oculomotor circuits in the brain, we hypothesized that similar remapping effects might result from attentional displacements without overt eye movements. We tested this hypothesis in right-brain damaged patients with and without left neglect in a visuo-spatial memory task. As predicted, neglect patients showed a selective deficit in location memory following an exogenous attentional shift caused by a brief flash in the periphery of their right (but not left) visual field. We conclude that an attentional displacement without eye movements is sufficient to remap spatial representations across hemifields, and that this process is impaired in neglect patients when a location has to be transferred to the neglected/left side relative to current gaze or attention focus. More generally, these results support the notion of neural overlap between oculomotor and attentional mechanisms, and confirm a role for impaired remapping in the neglect syndrome, wherein spatial representations of contralesional locations may fail to be maintained during active attentional behavior.

Task-irrelevant distractors in the delay period interfere selectively with visual short-term memory for spatial locations

Visual short-term memory (VSTM) enables the representation of information in a readily accessible state. VSTM is typically conceptualized as a form of "active" storage that is resistant to interference or disruption, yet several recent studies have shown that under some circumstances task-irrelevant distractors may indeed disrupt performance. Here, we investigated how task-irrelevant visual distractors affected VSTM by asking whether distractors induce a general loss of remembered information or selectively interfere with memory representations. In a VSTM task, participants recalled the spatial location of a target visual stimulus after a delay in which distractors were presented on 75% of trials. Notably, the distractor's eccentricity always matched the eccentricity of the target, while in the critical conditions the distractor's angular position was shifted either clockwise or counterclockwise relative to the target. We then computed estimates of recall error for both eccentricity and polar angle. A general interference model would predict an effect of distractors on both polar angle and eccentricity errors, while a selective interference model would predict effects of distractors on angle but not on eccentricity errors. Results showed that for stimulus angle there was an increase in the magnitude and variability of recall errors. However, distractors had no effect on estimates of stimulus eccentricity. Our results suggest that distractors selectively interfere with VSTM for spatial locations.

Neuronal substrates of Corsi Block span: Lesion symptom mapping analyses in relation to attentional competition and spatial bias

Spatial working memory problems are frequently reported following brain damage within both left and right hemispheres but with the severity often being grater in individuals with right hemisphere lesions. Clinically, deficits in spatial working memory have also been noted in patients with visuospatial disorders such as unilateral neglect. Here, we examined neural substrates of short-term memory for spatial locations based on the Corsi Block tapping task and the relationship with the visuospatial deficits of neglect and extinction in a group of chronic neuropsychological patients. Principal Component Analysis (PCA) was used to distinguish shared and dissociate functional components. The neural substrates of spatial short-term memory deficits and the components identified by PCA were examined using whole brain voxel-based morphometry and tract-wise lesion deficits analyses. We found that bilateral lesions within occipital cortex (middle occipital gyrus) and right posterior parietal cortex, along with disconnection of the right parieto-temporal segment of arcuate fasciculus, were associated with low spatial memory span. A single component revealed by PCA accounted for over half of the variance and was linked to damage to right posterior brain regions (temporo-parietal junction, the inferior parietal lobule and middle temporal gyrus extending into middle occipital gyrus). We also found link to disconnections within several association pathways including the superior longitudinal fasciculus, arcuate fasciculus, inferior fronto-occipital fasciculus and inferior longitudinal fasciculus. These results indicate that different visuospatial deficits converge into a single component mapped within posterior parietal areas and fronto-parietal white matter pathways. Furthermore, the data presented here fit with the role of posterior parietal cortex/temporo-parietal junction in maintaining a map of salient locations in space, with Corsi Block performance being impaired when the spatial map is damaged.

Input, Retention, and Output Factors Affecting Adult Age Differences in Visuospatial Short-Term Memory

The sources of age differences in short-term memory for spatial locations were explored in 2 experiments that examined factors related to input, to maintenance, and to output. In each experiment, 4 dots were presented briefly, followed after a retention interval by a probe dot, which was judged to either match or not match one of the 4 memory-set dots. Results showed that poorer performance by older adults could be attributed independently to reduced visual acuity, to less effective use of rehearsal strategies, and to differences in response biases.

Deletion of the GluA1 AMPA receptor subunit alters the expression of short-term memory

Deletion of the GluA1 AMPA receptor subunit selectively impairs short-term memory for spatial locations. We further investigated this deficit by examining memory for discrete nonspatial visual stimuli in an operant chamber. Unconditioned suppression of magazine responding to visual stimuli was measured in wild-type and GluA1 knockout mice. Wild-type mice showed less suppression to a stimulus that had been presented recently than to a stimulus that had not. GluA1 knockout mice, however, showed greater suppression to a recent stimulus than to a nonrecent stimulus. Thus, GluA1 is not necessary for encoding, but affects the way that short-term memory is expressed.

Electrolytic lesions of the ventral subiculum weakly alter spatial memory but potentiate amphetamine-induced locomotion

Adult Long–Evans male rats were subjected to electrolytic lesions of the ventral subiculum, and tested for locomotor activity in the home cage, reference and working memory in the water maze, working memory in the radial maze, and d-amphetamine-induced locomotion (1 mg/kg, i.p.). When compared to their sham-operated counterparts, lesioned rats showed nocturnal hyperactivity, no reference memory deficit, but working memory was impaired in the water maze and during the initial stage of radial-maze testing. Their locomotor responsiveness to d-amphetamine was exagerated. Histological verifications confirmed lesions in the ventral subiculum. Material stained for acetylcholinesterase activity indicated septohippocampal and commissural/associational sprouting, accounting for partial damage to the perforant paths. These results showed that ventral subiculum lesions (i) do not alter the capability of rats to learn repeatedly presented spatial information, and (ii) impair, but do not prevent, spatial working memory, suggesting that the ventral subiculum is preferentially involved in short-term memory for spatial locations. Given the electrolytic nature of the lesion, the lesion-induced potentiation of the locomotor response to amphetamine is probably easier explained by partial disruption of the perforant paths than by damage to neurons of the ventral subiculum.

The effect of visual similarity on short-term memory for spatial location: Implications for the capacity of visual short-term memory

Evidence from the recency effect suggests that visual short-term memory is limited to preserving information about a single pattern. Three experiments explored the capacity of visual short-term memory using a task which involved presenting a series of patterns in a random spatio-temporal sequence and probing memory for the spatial location of one of them. Experiment 1 used sequences of quasi-random block patterns which were either visually similar or dissimilar. Serial position curves showed a single-item recency effect. However, there was also a deleterious effect of visual similarity for the earlier patterns, indicating that visual short-term memory was supporting their retention. Experiment 2 showed that performance was unaffected by articulatory suppression, confirming that phonological coding is not an important factor in the localisation task. Experiment 3 switched to letter stimuli and, because of the known tendency for this type of stimulus to be phonologically recoded, required articulatory suppression. Letters were shown in a customised form in sequences which were either visually similar or visually dissimilar. The results replicated experiment 1 in showing restricted recency combined with an effect of visual similarity extending across earlier list items. When the same letters were shown in standard form, the recency effect remained but the similarity effect disappeared, ruling out possible interpretations in terms of semantic as well as phonological coding. It is concluded that the recency effect gives a misleading indication of the capacity of visual short-term memory. The visual similarity effect suggests that it is capable of supporting the retention of several patterns.

Further support for the “drift” model of pigeons' short-term memory for spatial location

The Drift Model is a conception of animals' short-term memory process as manifested in tasks such as delayed matching to sample. The model has four main assumptions. First, an attention focus or pointer moves through memory space representing the information that must be remembered. Second, during sample presentation, the pointer migrates in the direction of memory space representing the sample. Third, during delays (i.e., retention intervals), the pointer drifts in a random walk manner through memory space. Fourth, during the choice phase, subjects choose the alternative in memory space closest to the pointer. The model successfully accounts for many aspects of rats' (Roitblat & Harley, 1988) and pigeons' (Wilkie & Kennedy, 1987) short-term memory for spatial location. In the present research two explicit predictions were derived from the model, tested using pigeons in a delayed matching of key location task, and confirmed.

Short-term memory for spatial location in goal-directed locomotion

A blind walking study was conducted to examine the nature of the representation that subjects use to guide goal-directed locomotion. Subjects walked blindfolded to targets 4,8, and 12 m away, either immediately after visual occlusion or following a 2-sec or 30-sec no-vision delay. On half of the trials, subjects were cued as to target prior to visual occlusion; on the other trials, the specific target was identified after visual occlusion, just prior to walking. Although consistency in target acquisition was influenced by both distance and delay, prior knowledge as to target had no impact on error. These results suggest that subjects remember/forget the general spatial layout of the task environment as opposed to a specific target location.

The effects of time and distance on accuracy of target-directed locomotion: does an accurate short-term memory for spatial location exist?

The present study was an attempt to replicate the findings of an influential set of experiments by Thomson (1980, 1983) in which he demonstrated a highly accurate but transitory short-term memory for target location during locomotion. No evidence of Thomson's rapidly decaying 8 s short-term memory was found in either of the two experiments presented here. The distance to the target, not the elapsed time, was found to be the major variable affecting the accuracy of walks made without the benefit of visual feedback; as target distance increased so did locomotor error. Increasing the elapsed time to more than 8 s between viewing the target and reaching the vicinity of the target had no effect on the accuracy of walks made with eyes closed. When the elapsed time was greater than 30 s, however, performance began to deteriorate. These results suggest, in sharp contrast to Thomson's experiments, that short-term memory for target location decays rather slowly during locomotion. In this regard, short-term memory in locomotor tasks appears to be little different from the kinds of short-term memory associated with other motor acts.