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.     

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.     

Reproduction of End-Location and Distance of Movement in Early and Later Blinded Subjects

This study examined the ability of early and later blinded subjects to reproduce the end location and distance of preselected arm movements of two different amplitudes (approximately 30 degrees and approximately 60 degrees). Both groups were found to reproduce end location with greater accuracy and less variability than distance. The early blinded subjects were less accurate however and more variable in their reproductions of both movement cues than the later blinded subjects. The complications of these findings for the role of visual representation in memory for movement are discussed.     

Reproduction of end-location and distance of movement in early and later blinded subjects

This study examined the ability of early and later blinded subjects to reproduce the end location and distance of preselected arm movements of two different amplitudes (approximately 30 degrees and approximately 60 degrees). Both groups were found to reproduce end location with greater accuracy and less variability than distance. The early blinded subjects were less accurate however, and more variable in their reproductions of both movement cues than the later blinded subjects. The complications of these findings for the role of visual representation in memory for movement are discussed.     

The role of visual attention in saccadic eye movements

The relationship between saccadic eye movements and covert orienting of visual spatial attention was investigated in two experiments. In the first experiment, subjects were required to make a saccade to a specified location while also detecting a visual target presented just prior to the eye movement. Detection accuracy was highest when the location of the target coincided with the location of the saccade, suggesting that subjects use spatial attention in the programming and/or execution of saccadic eye movements. In the second experiment, subjects were explicitly directed to attend to a particular location and to make a saccade to the same location or to a different one. Superior target detection occurred at the saccade location regardless of attention instructions. This finding shows that subjects cannot move their eyes to one location and attend to a different one. The results of these experiments suggest that visuospatial attention is an important mechanism in generating voluntary saccadic eye movements.     

Feedback versus motor programming in the control of aimed movements.

In the Fitts paradigm the subject moves a stylus to the left or right of an initial rest position to reach targets that vary in size and in distance from the initial position. The classic finding for relatively long movements is that movement time, measured from leaving the initial position until contact with the target, depends on both distance and target size according to a relationship known as "Fitts' law." By contrast, reaction time, measured from the signal to move until the stylus leaves the initial position, is independent of these parameters. While replicating these results for long movements, the present data show a different pattern for very short movements, for which Fitts' law no longer holds and for which reaction time increases as the size of the target is decreased. These findings were interpreted as implying that long movements are under feedback control, whereas short movements are predominately programmed and ballistic. This conclusion was supported by the additional finding that elimination of visual feedback was more disruptive to the long than to the short movements.     

Scaling Estimates of Amplitude for Movements Without Visual Guidance

Three groups of subjects were involved in estimating movement amplitudes. Two of these groups used the method of estimation, labeling the amplitudes of simple linear movements in inches. One group made active movements, the other experienced passive movement of the arm. The third group, using the method of production, attempted to move the distance required by the experimenter’s label. Performance was described in terms of absolute, algebraic, and intrasubject variable error. No striking differences were noted between the three task groups, but males and females differed systematically. Females tended to over-estimate and males to underestimate the distances moved. Lack of evidence for any range effect suggests that subjects were operating from relatively stable perceptual traces, accessed by the verbal labels, rather than from memory traces of previous estimates of the same amplitudes.     

Hand preference, practice order, and spatial assimilations in rapid bimanual movement

When subjects make rapid bimanual aiming movements over different distances, spatial assimilations are shown; the shorter distance limb overshoots when paired with a longer distance limb. Recent research has also shown spatial assimilations to be greater in the nonpreferred left limb of right-handed subjects, but it is not known whether the increased spatial assimilations represent a handedness effect or one of hemispheric lateralization of motor control. To determine the nature of the asymmetric effect, left- (n = 32) and right- (n = 60) handed subjects part practiced, then whole practiced, short (20 degrees ) and long 60 degrees ) reversal movements. During whole practice, both groups showed spatial assimilations in the shorter distance limb, particularly when the left limb performed the short movement. This asymmetry was greatest for right-handed subjects, but left-handed subjects showed smaller, but systematic effects, providing moderate support for the hypothesis that the asymmetric effect is due to hemispheric lateralization of motor control. All interlimb differences in spatial accuracy for the short and long movements were eliminated with practice, however, suggesting the asymmetric effect was temporary as well. In addition, subjects who part practiced the long movement just prior to whole practice showed greater overshooting in the short distance limb compared with subjects who followed the other practice order throughout whole practice and the no-KR retention trials. Such findings suggest that the part-practice order of bimanual tasks can directionally bias whole-task performance.     

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.     

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.     

The role of playing and efference in the recall location and distance cues in short-term motor memory

Previous studies have suggested that the superior accuracy of preselected (subject-defined) over constrained (experimenter-defined) movements is due to both the availability of a movement plan and efferent-command information. The present experiment examined the contribution of the planning and efferent components to the preselection effect in a location and a distance task. The availability of a movement plan was manipulated by providing preselected and constrained groups of subjects with a rehearsal movement. Furthermore, the amount of efferent information available was varied by requiring both active and passive rehearsal movements. The results suggested that while strategy alone is responsible for the superiority of preselected location, both strategy and efferent information underlie the superiority of preselected distance reproduction.     

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.     

Separate movement planning and spatial assimilation effects in sequential bimanual aiming movements

This study extended earlier work by showing spatial assimilations in sequential bimanual aiming movements when the participant preplanned only the first movement of a two-movement sequence. Right-handed participants (n=20, aged 18 to 22 years) made rapid lever reversals of 20 degrees and 60 degrees singly and sequentially with an intermovement interval of 2.5 sec. Following blocked single practice of both movements in each hand (15 trials each), two sets of 30 sequential practice trials were completed. The sequences began with either the long or the short movement and the participant always knew the goal of the first movement. During the intermovement interval, the experimenter gave instructions to complete the sequence with a short movement, a long movement, or no movement in a random order. Compared to the single trials, both movements in the sequence overshot the short-distance and undershot the long-distance goal. Spatial errors increased when a change in the movement goal was required for the second movement in the sequence. The experiment demonstrated that separate planning of sequential aiming movements can reduce spatial assimilation effects, but interference due to practice organization and switching the task's goal must also be overcome in order to produce accurate aiming movements.     

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.     

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.     

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.     

Cognitive Strategies and Short-term Memory for Movement Distance and Location

A number of researchers (e.g. Kerr, 1978; Walsh, Russell, Imanaka, & James, 1979) have previously demonstrated interference between location and distance information in motor short-term memory. This interference manifests itself in a characteristic pattern of undershooting and overshooting, with reproduction movement location being drawn in the direction of criterion movement distance and, conversely, the distance of reproduction movements being influenced by the terminal location of the criterion movement. We investigated the effects of different cognitive strategies upon the appearance of this location-distance interference during the reproduction of movement location (Experiment 1) and distance (Experiments 2 and 3) in a linear arm positioning task. Experiment 1 compared performance in location reproduction between two strategy groups differing in the availability of explicit information about the change in starting position. The characteristic undershooting-overshooting interference pattern was observed for the group without the explicit information about the change in starting position but disappeared for the group in which explicit information about the change in starting position was provided. Experiment 2 examined the systematic undershooting-overshooting pattern in distance reproduction for a location strategy (involving some extrapolation of the start and end locations), a counting strategy, and a distance sense strategy (involving the use of visual imagery). The systematic response bias pattern disappeared when the subjects used a location strategy but was clearly observed for the subjects using the other two strategies. This finding was generally confirmed by Experiment 3, which showed a typical undershooting-overshooting pattern in distance reproduction for a counting/distance sense strategy but not for two location strategies (a general location and an explicit location strategy). The location strategies differed in the availability of explicit information about starting and end locations for both the criterion and reproduction movements. The results from these three experiments indicate that explicit information about the start andlor end locations prevents the usual interference between location and distance information from arising in movement reproduction. The notions of automatic and controlled processing and cerebral hemispheric specialization are discussed as potential explanations of these results and of the interference typically observed in motor short-term memory between distance and location information.     

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.     

Visual control of movement patterns and the grammar of action

In this experiment adult subjects copied three types of material (letters, reversed letters and geometric shapes) with and without sight of the hand and the writing trace. Without vision the number of movement segments decreased and the sequence and direction of movements were altered. This means that subjects did not use a fixed stored representation to produce items nor did they obey the rules of Goodnow and Levine's (1973) grammar of action. When spatial location is made more difficult by the removal of vision, movement production is simplified to reduce the number of relocations required. The use of consistent directions of movement depends on the ability to use visual control of spatial location.     

Stimulus Generalization and the Peak Shift with Movement Stimuli

Stimulus generalization is suggested as an alternative method for examination of the “novelty? problem in motor learning. These experiments demonstrated that stimulus generalization occurs using simple movements as stimuli. The phenomenon of the “peak shift? in post-discrimination generalization gradients was also examined. The first experiment demonstrated that a peak shift occurred using linear movements as stimuli and that the magnitude of the peak shift increased as the difference between the training stimuli decreased. The second experiment showed similar results when the stimuli consisted of a range of movements rather than a single movement length. The final experiment provided evidence that perception of movement length is influenced by the magnitude of an immediately preceding movement. The relevance of these studies to current motor-learning theory is discussed.