Retention Characteristics of Motor Short-Term Memory Cues

The retention characteristics of several cues thought to underlie movement reproduction ability were examined and the results were discussed in terms of two models of motor short-term memory (Laabs, 1973; Pepper & Herman, 1970). Trace decay was indexed by constant error and not variable error. It appeared that the movement cues studied all had access to the central processing capacity in that forgetting did not occur until rehearsal was blocked by the introduction of a secondary task. However, there was some evidence to indicate that different cues are centrally represented in varying degrees of exactness. In this respect reliance on active movement cues and location cues produced better reproduction than passive movement and distance cues, respectively. The existence of an adaptation level established from the range of movement utilized was supported, and short movements were more dependent on central processing capacity than were long movements.     

Memory for Constrained and Preselected Movement Location and Distance

These experiments assessed the interrelationship between location and distance cues in the coding of movements. In separate experiments subjects recalled either the terminal location or the distance of constrained (Experiment 1) or preselected (Experiment 2) movements following a 15-sec retention interval. Changes in direction amd amplitude of starting position were used to ascertain whether recall errors were related to these changes. The findings of both experiments indicated that location and distance were recalled with similar accuracy when the starting position was identical for the criterion and recall movement. However, analysis of constant errors when the recall starting position was varied in either direction clearly indicated neither terminal location nor distance are coded independently, and memory for movement is based on an interaction between these cues.     

Retention characteristics of movement rate information

The retention characteristics of fast and slow movements were investigated in two experiments. Experiment 1 examined the reproduction of either fast or slow preselected movement rates after 0-sec rest, 15-sec rest or a 15-sec filled delay. Both fast and slow movement rates were rehearsable. Experiment 2 examined reproduction accuracy after subjects were required to perform a competing secondary task during the production of fast and slow movements. Although the secondary task degraded the reproduction of slow movements, it had no apparent effect upon the reproduction of fast movements. These results were interpreted as indicating partial support for Jones' (1974) notion of central monitoring of efference, and suggested that the contribution of proprioceptive feedback to movement control varies as a function of movement rate.     

The coding of constrained and preselected movement distance: Same-limb versus switched-limb reproduction

Three experiments were conducted to investigate the codes subserving the retention of movement extent information. Each experiment compared preselected and constrained movements in two independent movement tasks: same-limb reproduction and switched-limb reproduction. When movement direction was the same for both criterion and reproduction movements (experiment 1), same-limb reproduction was more accurate than switched-limb performance. With movement direction altered, however, switched-limb reproduction was equal to same-limb reproduction (experiment 2). These results were confirmed in experiment 3 which manipulated both movement direction and reproduction limb in a within-subject design. Furthermore, while preselected reproduction was superior to constrained reproduction in all three experiments, the two groups were not differentially affected by either the movement task or direction variables. The overall findings were interpreted as providing support for a multiple-cue memorial representation of movement extent and the notion of coding flexibility.     

Interference Between Location and Distance Information in Motor Short-Term Memory: The Respective Roles of Direct Kinesthetic Signals and Abstract Codes

Interference between location and distance information in motor short-term memory has been hypothesized on the basis of the systematic pattern of undershooting and overshooting in movement reproduction that occurs when the starting position for reproduction movements is shifted. To determine the possible contribution of limb-specific kinesthetic information to this systematic undershooting-overshooting pattern, we compared the reproduction of linear arm positioning movements performed under either same-limb or switched-limb conditions. Ten subjects were assigned to either a location or distance cue condition, and each subject completed a total of 40 trials, 20 under same-limb and 20 under switched-limb conditions. Each trial consisted of criterion and reproduction movements, separated by a 10-s retention interval. The starting position for the reproduction movement was shifted by 0, 2, or 4 cm in either direction from that of the criterion movement. The systematic undershooting-overshooting pattern, which occurs when either the movement location or distance is reproduced, arose under both the same-limb and switched-limb conditions, suggesting that the primary cause of the location-distance interference is not limb-specific kinesthetic information. Rather, more abstract information in the form of a conceptual memory code appears to be the probable cause of the location distance interference phenomenon.     

The Effect of Interpolated Motor Activity on the Short-Term Retention of Movement Distance and End-Location

The effect of an interpolated movement on the recall of a blind, lever-positioning movement was assessed separately for the reproduction cues of distance and end-location. Both cues showed the context effect of assimilation, that is, the end-location of the interpolated movement caused directional biasing of the algebraic or constant error (CE) for location reproduction while the length of the interpolated movement caused similar directional biasing for distance reproduction. Variability about algebraic error (VE) was used to assess forgetting. There was no change in VE for location reproduction, and an increase in VE for distance reproduction was limited to the relatively large movements. Thus, an interpolated movement that does not have to be remembered does not cause interference with the retention of location information, but does cause some interference with the retention of distance information. The findings are discussed in relation to a model of motor short-term memory which incorporates both CE and VE.     

Attentional requirements for location and distance of movement: encoding and recognition

The purpose of this experiment was to study the early processing stages of encoding and recognition of slow movement in a short-term motor-memory paradigm. These stages were examined by determining whether Laabs' (1973) differential decay rates for location of movement and distance of movement could be replicated when the interfering activity was performed during the criterion and replication movements. 20 subjects performed a linear-positioning task in a 2 X 2 X 2 (count X movement type X retention interval) experimental design. 10 subjects in one condition counted backwards by 3s during the criterion and replication movements. There were no detrimental effects for location and distance-cue reproduction when attention was shared with counting backwards. Like Laabs' results, location of movement was maintained over the 15-sec. interval while distance of movement spontaneously changed. These results supported the notion that the early stages of encoding and recognition of cues for movement can occur unaffected by a secondary task.     

Target-related coupling in bimanual reaching movements

While bimanual interference effects can be observed when symbolic cues indicate the parameter values of simultaneous reaching movements, these effects disappear under conditions in which the target locations of two movements are cued directly. The present study investigates the generalizability of these target-location cuing benefits to conditions in which symbolic cues are used to indicate target locations (i.e., the end points of bimanual movements). Participants were asked to move to two of four possible target locations, being located either at the same and different distances (Experiment 1), or in the same and different directions (Experiment 2). Circles and crosses served as symbolic target-location cues and were arranged in a symmetric or non-symmetric fashion over the four target locations. Each trial was preceded by a variable precuing interval. Results revealed faster initiation times for equivalent as compared to non-equivalent target locations (same vs. different cues). Moreover, the time course of prepartion suggests that this effect is in fact due to target-equivalence and not to cue-similarity. Bimanual interference relative to movement parameter values was not observed. These findings suggest that cuing target locations can dominate potential intermanual interference effects during the concurrent programming of different movement parameter values.     

Preselection in short-term motor memory.

Recent studies by Jones (1974) have posited that accurate movements in short-term motor memory (STMM) are mediated by the subject's ability to preset effector mechanisms and monitor their efferent output. Three experiments were conducted to examine this hypothesis. Experiment 1 involved comparisons between the reproduction of the end-location and the reproduction of the distance of a preselected movement. The results revealed that preselected location was superior to preselected distance, indicating that the efference attached to movement extent was not primary. Experiment 2 examined whether location cues were primarily encoded independent of the movement presentation mode. The subjects recalled target locations under preselected, constrained, and passive movement conditions. Recall in the preselected condition was superior to that in the constrained and passive conditions, which showed no difference, suggesting that afferent location information per se was not totally responsible for recall accuracy. Experiment 3 examined the processing requirements of preselected, constrained, and passive location information by filling the retention interval with interpolated processing activity. While preselected location was clearly superior, the three conditions were not differentially affected by processing activity. These overall findings were interpreted as contrary to Jones (1974) and pointed to the importance of preselection in short-term motor memory.     

Memory for movement: Interaction of location and distance cues and imagery ability

The present experiments examined the role of imagery ability in recall of either the terminal location or the distance of a preselected horizontal linear movement following changes in the recall starting position. Subjects were selected on the basis of their scores on a shortened version of the Betts Questionnaire upon Mental Imagery (Betts Q.M.I., Sheehan 1967). Both high and low imagers were assigned to one of four groups, HIL, LIL, HID, LID, the last letter indicating the movement cue (terminal location or distance moved) to be recalled. Recall of the appropriate movement cue from one of four new recall starting positions occurred after either a 5-sec or 30-sec unfilled retention interval. Analysis of constant error indicated all groups were unable to recall the specified movement cue independent of the other source of information, even when subjects were given explicit instructions to utilise an imagery strategy. The data corroborate our earlier findings that memory for self paced movements is based on an interaction of location and distance cues derived from the criterion movement.     

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.     

Decay and interference effects in motor short-term memory

Trace decay and interference effects in motor short-term memory were investigated by contrasting the predictions of two recent models (Pepper and Herman 1970; Laabs 1973) in regard to these two variables. Laabs' prediction that forgetting in motor short-term memory is indexed by greater variability of reproduction was supported in that movement reproduction after a 20 sec retention interval, either filled or unfilled, produced greater variable error. Further, his model was again supported in that analysis of constant error over five movement extents indicated interference effects through formation of an adaptation level which caused short movements to be overshot and long movements to be undershot. Pepper and Herman's concept of spontaneous trace decay indexed by a negative shift in constant error was not supported as was their prediction that interpolated activity would alter the strength of the criterion trace through an assimilation process. Finally, some evidence was found supporting the view that a memory trace can be strengthened through proprioceptive feedback entering through an unattended channel.     

Criterion movements in motor short-term memory experiments

Analysis of both the criterion and reproduction movements from a motor short-term memory experiment using preselected movement is presented. The movement cues under imvestigation, location and distance, were found to interact significantly with amplitude for both the criterion and reproduction movements. It seems that movement cue affects the amplitude of criterion as well as reproduction movements. Thus previous findings by Gundry (1975) are replicated and extended. An increase in a central tendency effect over trials was found which indicated that the criterion movements were effected by proceding movements. The theoretical and methodological implications of these findings are discussed.     

The influence of movement cues on intermanual interactions

In two experiments, we studied intermanual interactions in bimanual reversal movements and bimanual aiming movements. Targets were presented on a monitor or directly on the table on which the movements were produced. Amplitudes for each hand were cued symbolically or spatially either in advance of an imperative signal or simultaneous with it. In contrast to findings of Diedrichsen et al. (Psychological Science, 12, 493–498, 2001), reaction times for different-amplitude movements were longer than for same-amplitude movements both for symbolic and spatial cues presented on the monitor and directly on the table. However, with symbolic cues the effect of the relation between target amplitudes was considerably stronger than with spatial cues, no matter where the cues were presented. Intermanual correlations of amplitudes, movement times, and reaction times were smaller with different than with same target amplitudes, and this modulation was more pronounced when targets and cues were presented on the monitor than when they were presented on the table. The findings are taken to suggest that the basic reaction-time disadvantage of different-amplitude movements results from interference between concurrent processes of amplitude specification. Additional factors like interference between concurrent processes of mapping cues on movement characteristics may add strongly to it.     

Reproducing the End Location of a Positioning Movement

Two experiments were conducted in an attempt to determine the conditions under which shifts in the starting position of a linear positioning response influenced the reproduction of the end location of movements of various lengths. In Experiment 1, response bias (i.e., shift in constant error) was affected by the direction of the shift in starting position between presentation and recall. For short (20 cm) and medium (50 cm) length movements, this relationship was evident regardless of hand used (left or right), direction of the movement (left to right or right to left), and length of the retention interval (5 or 45 s). However, no relation between response bias and the direction of starting position shifts was apparent for long (80 cm) movements. The results of Experiment 2 in which more movement lengths were used revealed a response bias that corresponded to shifts in starting position primarily during the first few reproductions of the two shortest movements (20 and 30 cm). However, no systematic bias was evident for any length movement after three reproduction attempts. Possible strategies used by subjects to reproduce the end location of movements of various lengths were discussed.     

Reproducing the end location of a positioning movement: the long and short of it

Two experiments were conducted in an attempt to determine the conditions under which shifts in the starting position of a linear positioning response influenced the reproduction of the end location of movements of various lengths. In Experiment 1, response bias (i.e., shift in constant error) was affected by the direction of the shift in starting position between presentation and recall. For short (20 cm) and medium (50 cm) length movements, this relationship was evident regardless of hand used (left or right), direction of the movement (left to right or right to left), and length of the retention interval (5 or 45 s). However, no relation between response bias and the direction of the starting position shifts was apparent for long (80 cm) movements. The results of Experiment 2 in which more movement lengths were used revealed a response bias that corresponded to shifts in starting position primarily during the first few reproductions of the two shortest movements (20 and 30 cm). However, no systematic bias was evident for any length movement after three reproduction attempts. Possible strategies used by subjects to reproduce the end location of movements of various lengths were discussed.     

Encoding specificity principle in motor short-term memory for movement extent

The hypothesis was tested that, when the mode of presentation matches the mode of reproduction in memory for movement extent, there is less error in reproduction than when the modes are not matched. Female undergraduates (n = 24) were tested under active and passive criterion movements presented either under preselected or constrained conditions. All subjects underwent 36 trials involving the combination of three retention conditions (immediate, 20-sec unfilled, and 20-sec filled) and two reproduction conditions (active and passive). Results for absolute error showed that for constrained presentations, when the mode of presentation and the mode of reproduction were the same, accuracy was greater than when the modes of presentation and reproduction were different.     

Preselection and response biasing in short-term motor memory

Two experiments were performed comparing preselected (subject defined) and constrained (experimenter defined) movements. In the first experiment, subjects made reproduction responses immediately or under unfilled and filled 15-sec retention intervals. Results indicated that recall of preselected movements was clearly superior until the interpolation of information processing activity. In addition, preselected movements demonstrated no forgetting over a 15-sec retention interval while constrained movements evidenced spontaneous memory lass, suggesting that preselected movements possess a stronger representation in memory. The second experiment examined this interpretation in a response biasing paradigm. Subjects made criterion responses under preselected or constrained conditions, while the interpolated movement was always in the constrained mode and ± 40 deg from the criterion. The subjects' task was to attend to both movements and recall each when instructed. While preselected recall was clearly superior' to constrained recall, response biasing was clearly evident in both. The failure to find differential biasing effects was discussed in terms of the relative trace strength hypothesis (Stelmach & Welsh, 1972).     

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.     

Effect of starting position on reproduction of movement: further evidence of interference between location and distance information

Two experiments done with a short-term memory paradigm examined the influence of shifts in the starting position on the reproduction of kinesthetic location (Exp. 1) and on distance cues (Exp. 2). We assessed possible causes of the systematic pattern of undershooting and overshooting as related to the shift in the starting position. In each experiment, two groups of 10 students were given 25 trials, and each had criterion and reproduction tasks involving linear-positioning movements with a 10-sec. retention interval. Each experiment had two independent variables, the group of subjects and the shift in the starting position. The two groups differed in the possible sources of information, the distance moved (Exp. 1) or the end-location (Exp. 2), which were assumed to cause undershooting and overshooting during reproduction. Analysis showed that the information about the distance moved may produce undershooting and overshooting in reproduction of the end-location (Exp. 2). Also, the information about the end-location may produce undershooting and overshooting in reproduction of the distance moved (Exp. 2). The findings were further evidence of interference between location and distance cues in motor short-term memory.