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Decay and interference effects in motor short-term memory
Acta Psychologica 0 North-Holland
39 (1975), 217-223. Publishing Company.
DECAY AND INTERFERENCE SHORT-TERM MEMORY
EFFECTS
IN MOTOR
R. G. MARTENIUK and G. L. DIEWERT University of Waterloo, Waterloo, Ontatio, Canada Received
December
1974
Trace decay and interference effects in motor short-term memory were investigated by contrasting the predictions of two recent models (Pepper and Herman 1970; l_aabs 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 set retention interval, either tilled 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.
1. Introduction Two recent models of motor short-term memory (MSTM) predict different mechanisms underlying decay and interference in the reproduction of simple movements. One model by Pepper and Herman (1970) utilizes constant error (CE) as the index of both decay and interference. In terms of decay, the model predicts that all movement information spontaneously decays over a retention interval in the direction of lesser extent accounting for a CE shift in the negative direction. In addition, an assimilation mechanism is proposed to explain interference where the level of proprioceptive stimulation generated by an interpolated activity, like counting or moving, interacts with the decaying reference trace to produce an altered trace which S faithfully reproduces. The strength of this augmented trace is indexed by a shift in CE, either positive or negative in trend, corresponding to a mean
218
R. G. Marterliuk, G. L. Diewert /Decay
and interference
effects
proprioceptive level either greater or less than, respectively, the strength of the criterion trace. The other model (Laabs 1973) utilizes two different dependent measures to index decay and interference effects. Laabs visualizes a decaying trace as being a less stable reference for reproduction and hence postulates that reproductions should be more viable and appropriately indexed by variable error (VE). Interference effects for movement are explained in Laabs’ model by a type of adaptation theory (Helson 1964) where a movement is always influenced by an average movement or an adaptation level produced by the range of movements used by the E. Interference resulting from the adaptation level is indexed by CE since movements shorter than the adaptation level will be overshot and movements longer than the adaptation level will be undershot. The present study was designed to contrast several predictions of the above two models: first, does CE or VE index decay; second, does movement information containing position cues decay spontaneously; and third, does adaptation level, as envisaged by Laabs, or trace alteration effects, as postulated by Pepper and Herman, explain interference in movement reproduction? 2. Method 2.1. Subjects The Ss (N = 48) were 24 male and 24 female undergraduates at the University of British Columbia who volunteered to participate. All Ss were task naive, right hand dominant and ranged in age from 17-24 years.
2.2. Apparatus The movement apparatus consisted of a half circle of masonite board with an arc, calibrated in half degrees, drawn on it. A lever was attached to a near frictionless pivot at the mid-point of the chord describing the arc. The S moved the lever in the horizontal plane by means of a handle which could be adjusted along the length of the lever.
2.3. Design The design was a 4 were randomly assigned
X
2 X 5 factorial with repeated measures over the last factor. The 48 Ss to the four independent groups; an equal number of males and females
R. G. Marteniuk, G. L. Diewert /Decay and interference effects
219
were assigned to each group and the effect of sex was analysed as the second factor. After the analysis revealed no effect on sex the data were regrouped to give a 4 X 5 factorial design. The four between S variables were four conditions of movement reproduction. The five within S variables were different lengths of criterion movement. Each S received five trials of each movement with the movements appearing randomly in blocks of five trials with the restriction that each movement appear once in each block.
2.4. Procedwe All Ss were blindfolded before they entered the testing area and ear covers were worn to eliminate auditory cues. Male 5s were required to strip from the waist up, while females were provided with a sleeveless shirt. This precaution was taken to prevent proprioceptive cues arising from contact with clothing. S was placed in a standard position at the apparatus which came to approximately a height halfway between the shoulders and hips of the standing S. The starting position of the right arm for all movements was approximately 80” adduction. The S was required to move the lever by grasping the handle and rotating his shoulder joint toward his body resulting in a movement in the horizontal plane. The S moved the lever until it reached a physical stop determined by E at one of the five movement distances (15”, 30”, 45”, 60” and 75”). The S held this position for 2 set and then returned the lever to the start. After the appropriate retention interval, the S attempted to reproduce the criterion movement without the aid of the block. Each S was given 3 practice trials and then the 25 experimental trials, each trial consisting of a criterion and a reproduction. The algebraic error, to the nearest half degree, was recorded for each trial. The intertrial interval was 15 set and S was allowed to disengage and rest his arm at his side during this time. Condition 1 involved immediate reproduction in that the S attempted to reproduce the criterion movement as soon as the lever had been returned from the block. Condition 2 contained a 20 set retention interval between presentation of the criterion and its reproduction during which time S was instructed to think about the criterion movement both in its extent and its terminal position. Condition 3 was identical to condition 2 except S was required to count backwards by threes from a randomly chosen three digit number presented to him after the criterion movement. Condition 4 again involved a 20 set retention interval in which S counted backwards for the first 7 set, then he was required, while he kept counting, to move the lever to the block that remained at the criterion location. After this, he returned the lever to the starting position, still maintaining his counting, and he then continued to count until the reproduction was requested at the end of the 20 set retention interval.
3. Results Two dependent measures were calculated and evaluated by ANOVA: CE was the mean of the 5 algebraic errors at each movement, and VE was the standard deviation of the algebraic errors at each movement. The analysis of CE revealed a significant main effect of Movement Length with F (4,176) = 14.00, p < 0.001. The main effect of Conditions (F (3,44) = 0.49, p > 0.05) and the Conditions X Movements interaction (F (12,176) = 1.57, p > 0.05) failed to reach significance. In the analysis of VE both the main effects of Movement (F (4,176) = 7.94, p < 0.001) and Conditions (F (3,44) = 7.14, p < 0.001) were significant. Again the Conditions X Movements
220
R. G. Marten&k,
Table 1 Mean Constant
Errors in degrees
G. L. Diewert /Decay
for reproduction Movement
and interference
conditions
efyects
and movement
lengths.
lengths
Conditions
M,
M*
M,
M,
M,
Marginal
1. Immediate reproduction 2. 20 set rehearsal 3. 20 set counting
2.77 1.78 3.84
0.70 4.89 2.24
xi.25 -1.24 4.23
xl.90 -2.32 -3.69
-1.83 -1.06 -3.17
0.10 -0.74 -0.20
2.67 2.76
1.17 0.80
a.07 xl.45
1.09 -1.45
4.40 -1.61
0.89
4.
20 set counting movement Marginal means
Table 2 Mean Variable
means
+
Errors in degrees
for reproduction Movement
conditions
and movement
lengths.
lengths
Conditions
M,
M,
M,
M,
M,
Marginal
1. 2. 3. 4.
2.5 1 3.09 3.65
2.53 4.47 4.93
3.71 4.85 5.24
4.07 5.49 5.58
3.81 5.08 5.86
3.33 4.60 5.05
3.31 3.14
3.42 3.84
3.70 4.37
3.28 4.61
3.23 4.50
3.39
Immediate reproduction 20 set rehearsal 20 set counting 20 set counting + movement Marginal means
means
interaction was not significant (F (12,176) = 1.24, p > 0.05). A further post hoc comparison of the Condition means by the Scheffe method revealed the following: (a) the immediate reproduction condition was significantly less variable than both the 20 set rehearsal and 20 set counting conditions; and (b) the 20 set counting condition was significantly more variable than the 20 set counting + movement condition. All other single comparisons were not significant.
4. Discussion The first question of interest to be asked of the above data in terms of contrasting the models of Pepper and Herman (1970) and Laabs (1973), concerns whether CE or VE indexes decay. Pepper and Herman would predict that over an unfilled interval the trace would spontaneously decay and this would result in a negative shift in CE relative to the CE in immediate reproduction. The fact that the CEs of these two conditions in the present study (Conditions 1 and 2) were not statistically different does not support this prediction. Laabs, on the other hand, would predict that VE should differentiate an immediate repro-
R. G. Marteniuk,
G. L. Diewert /Decay
and interference
effects
221
duction condition from one where the retention interval was filled by an attention demanding mental activity (Condition 3). In this latter condition it would be expected that trace decay would occur and reproduction, since it was based ~ipon a weak or ill defined trace, would be more variable. This is in essence what occurred, and hence Laabs’ view would seem to be upheld. The second purpose of the present investigation was to determine if position cues could be retained over an unfilled retention interval. Laabs’ model predicts that these cues have access to the central processes and thus are capable of being coded and rehearsed. However since Condition 2 (unfilled 20 set retention interval) produced greater VE than Condition 1 (immediate reproduction) it would seem to contradict this prediction. This finding was unexpected since several other investigations (Posner 1967; Marteniuk and Roy 1972; Marteniuk 1973; Laabs 1973) have found that location cues were well retained over a retention interval. But a major difference between these studies and the present one was in the method of presentation of location information. In the earlier investigations, distance cues were made unreliable so S could only rely on the terminal location information for successful reproduction. The methodology of presenting movements in the present study was such so as to make both location and distance cues reliable sources of information. It may be in this case the distance information interfered with the retention of the location information. The final purpose of the present study was to contrast the views of Pepper & Herman and Laabs in terms of their predictions about interference in movement reproductions. A valid test of Pepper and Herman’s model involves comparing the CEs of Conditions 2, 3, and 4. Condition 3 involved counting backwards during the retention interval while Condition 4 involved counting and movement during the same time period. According to the model, the proprioceptive stimulation arising from these interpolated activities should have augmented the decaying memory trace and produced a CE more positive than in the comparable resting condition (in this case Condition 2). That CE failed to be differentiated among these three groups indicates a lack of support for the proposed model. One possible explanation for the null results may be derived from the methodology employed by Pepper and Herman. Their results may be unique to their experimental situation which consisted of force reproduction ranging from 1.70 to 4.25 kgms. Since there may be different retention and interference characteristics
222
R. G. Marteniuk, G. L. Diewert /Decay
and interference
effects
for force reproduction, their results may not be able to be generalized to movement reproduction. The fact that movement reproduction seems to yield different interference effects from those of force is supported by the present results, which seem to agree with Laabs’ concept of interference. In essence, the overshooting of short movements and undershooting of long movements observed in the present data is what would be expected if an adaptation level, or average movement, had been established. However, Laabs’ model would also predict that Condition 3 (counting backwards) should have produced a greater reliance on the adaptation level resulting in larger overshooting of short movements and larger undershooting of longer movements. That this did not occur detracts somewhat from the strong support previously given to Laabs’ model. From the above discussion it can be concluded that the results heavily support the view that VE is the index of trace decay in a movement reproduction task. In this respect it appears that Laabs’ concept of a decaying memory trace losing its precision and causing variability in reproduction is a viable one. Moreover, it is concluded that interference, of a proactive type, caused by the formation of an adaptation level can explain trends in CE over a range of movements S is working in. Again this is seen as support for Laabs’ model. One interesting finding of the present results, which cannot be explained by either model, is the equivalence of Conditions 1 and 4 in terms of VE. If VE is a valid measure of trace decay and counting and movement during the retention interval occupy the S’s central processing capacity there is no reason to expect the trace to be maintained to a level equal to that in immediate reproduction. Two explanations are offered for the low VE of this condition. First, the counting may not have occupied S’s attention completely and the results can be explained simply by repetition of the criterion movement during the retention interval. However, this seems unlikely since counting alone in Condition 3 produced significantly more variability when compared to Condition 1. Therefore since all Ss maintained counting while moving this explanation seems to be ruled out. The second interpretation of the above effect can be stated in terms of research by Norman (1968, 1969) who developed a memory model which states that material presented on a non-attended channel has access to short-term memory. Since the criterion trace is already
R. G. Marteniuk, G. L. Diewert /Decay
and interference
effects
223
present in short-term memory it may be that the proprioceptive feedback from the second movement, although not attended to, still gains access to memory and maintains the strength of the original trace.
References H&on, H., 1964. Adaptation level theory. New York: Harper and Row. Laabs, G. J., 1973. Retention characteristics of kinesthetic information. J. Exp. 168-177. Marteniuk, R. G., 1973. Retention characteristics of motor short-term memory Behav. 5,249-259. Marteniuk, R. G. and E. A. Roy, 1972. The codability of kinesthetic location information. Acta Psychol. 36,471-479. Norman, D. A., 1968. Toward a theory of memory and attention. Psychol. Rev. Norman, D. A., 1969. Memory while shadowing. Quart. J. Exp. Psychol. 21,85-93. Pepper, R. L. and L. M. Herman, 1970. Decay and interference effects in short-term a discrete motor act. J. Exp. Psychol. Monogr. Suppl. 83, l-18. Posner, M. L., 1967. Characteristics of visual and kinesthetic memory codes. J. 75,103-107.
Psychol.
100,
cues. J. Mot. and distance 75,522-536. retention
of
Exp. Psychol.
39 (1975), 217-223. Publishing Company.
DECAY AND INTERFERENCE SHORT-TERM MEMORY
EFFECTS
IN MOTOR
R. G. MARTENIUK and G. L. DIEWERT University of Waterloo, Waterloo, Ontatio, Canada Received
December
1974
Trace decay and interference effects in motor short-term memory were investigated by contrasting the predictions of two recent models (Pepper and Herman 1970; l_aabs 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 set retention interval, either tilled 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.
1. Introduction Two recent models of motor short-term memory (MSTM) predict different mechanisms underlying decay and interference in the reproduction of simple movements. One model by Pepper and Herman (1970) utilizes constant error (CE) as the index of both decay and interference. In terms of decay, the model predicts that all movement information spontaneously decays over a retention interval in the direction of lesser extent accounting for a CE shift in the negative direction. In addition, an assimilation mechanism is proposed to explain interference where the level of proprioceptive stimulation generated by an interpolated activity, like counting or moving, interacts with the decaying reference trace to produce an altered trace which S faithfully reproduces. The strength of this augmented trace is indexed by a shift in CE, either positive or negative in trend, corresponding to a mean
218
R. G. Marterliuk, G. L. Diewert /Decay
and interference
effects
proprioceptive level either greater or less than, respectively, the strength of the criterion trace. The other model (Laabs 1973) utilizes two different dependent measures to index decay and interference effects. Laabs visualizes a decaying trace as being a less stable reference for reproduction and hence postulates that reproductions should be more viable and appropriately indexed by variable error (VE). Interference effects for movement are explained in Laabs’ model by a type of adaptation theory (Helson 1964) where a movement is always influenced by an average movement or an adaptation level produced by the range of movements used by the E. Interference resulting from the adaptation level is indexed by CE since movements shorter than the adaptation level will be overshot and movements longer than the adaptation level will be undershot. The present study was designed to contrast several predictions of the above two models: first, does CE or VE index decay; second, does movement information containing position cues decay spontaneously; and third, does adaptation level, as envisaged by Laabs, or trace alteration effects, as postulated by Pepper and Herman, explain interference in movement reproduction? 2. Method 2.1. Subjects The Ss (N = 48) were 24 male and 24 female undergraduates at the University of British Columbia who volunteered to participate. All Ss were task naive, right hand dominant and ranged in age from 17-24 years.
2.2. Apparatus The movement apparatus consisted of a half circle of masonite board with an arc, calibrated in half degrees, drawn on it. A lever was attached to a near frictionless pivot at the mid-point of the chord describing the arc. The S moved the lever in the horizontal plane by means of a handle which could be adjusted along the length of the lever.
2.3. Design The design was a 4 were randomly assigned
X
2 X 5 factorial with repeated measures over the last factor. The 48 Ss to the four independent groups; an equal number of males and females
R. G. Marteniuk, G. L. Diewert /Decay and interference effects
219
were assigned to each group and the effect of sex was analysed as the second factor. After the analysis revealed no effect on sex the data were regrouped to give a 4 X 5 factorial design. The four between S variables were four conditions of movement reproduction. The five within S variables were different lengths of criterion movement. Each S received five trials of each movement with the movements appearing randomly in blocks of five trials with the restriction that each movement appear once in each block.
2.4. Procedwe All Ss were blindfolded before they entered the testing area and ear covers were worn to eliminate auditory cues. Male 5s were required to strip from the waist up, while females were provided with a sleeveless shirt. This precaution was taken to prevent proprioceptive cues arising from contact with clothing. S was placed in a standard position at the apparatus which came to approximately a height halfway between the shoulders and hips of the standing S. The starting position of the right arm for all movements was approximately 80” adduction. The S was required to move the lever by grasping the handle and rotating his shoulder joint toward his body resulting in a movement in the horizontal plane. The S moved the lever until it reached a physical stop determined by E at one of the five movement distances (15”, 30”, 45”, 60” and 75”). The S held this position for 2 set and then returned the lever to the start. After the appropriate retention interval, the S attempted to reproduce the criterion movement without the aid of the block. Each S was given 3 practice trials and then the 25 experimental trials, each trial consisting of a criterion and a reproduction. The algebraic error, to the nearest half degree, was recorded for each trial. The intertrial interval was 15 set and S was allowed to disengage and rest his arm at his side during this time. Condition 1 involved immediate reproduction in that the S attempted to reproduce the criterion movement as soon as the lever had been returned from the block. Condition 2 contained a 20 set retention interval between presentation of the criterion and its reproduction during which time S was instructed to think about the criterion movement both in its extent and its terminal position. Condition 3 was identical to condition 2 except S was required to count backwards by threes from a randomly chosen three digit number presented to him after the criterion movement. Condition 4 again involved a 20 set retention interval in which S counted backwards for the first 7 set, then he was required, while he kept counting, to move the lever to the block that remained at the criterion location. After this, he returned the lever to the starting position, still maintaining his counting, and he then continued to count until the reproduction was requested at the end of the 20 set retention interval.
3. Results Two dependent measures were calculated and evaluated by ANOVA: CE was the mean of the 5 algebraic errors at each movement, and VE was the standard deviation of the algebraic errors at each movement. The analysis of CE revealed a significant main effect of Movement Length with F (4,176) = 14.00, p < 0.001. The main effect of Conditions (F (3,44) = 0.49, p > 0.05) and the Conditions X Movements interaction (F (12,176) = 1.57, p > 0.05) failed to reach significance. In the analysis of VE both the main effects of Movement (F (4,176) = 7.94, p < 0.001) and Conditions (F (3,44) = 7.14, p < 0.001) were significant. Again the Conditions X Movements
220
R. G. Marten&k,
Table 1 Mean Constant
Errors in degrees
G. L. Diewert /Decay
for reproduction Movement
and interference
conditions
efyects
and movement
lengths.
lengths
Conditions
M,
M*
M,
M,
M,
Marginal
1. Immediate reproduction 2. 20 set rehearsal 3. 20 set counting
2.77 1.78 3.84
0.70 4.89 2.24
xi.25 -1.24 4.23
xl.90 -2.32 -3.69
-1.83 -1.06 -3.17
0.10 -0.74 -0.20
2.67 2.76
1.17 0.80
a.07 xl.45
1.09 -1.45
4.40 -1.61
0.89
4.
20 set counting movement Marginal means
Table 2 Mean Variable
means
+
Errors in degrees
for reproduction Movement
conditions
and movement
lengths.
lengths
Conditions
M,
M,
M,
M,
M,
Marginal
1. 2. 3. 4.
2.5 1 3.09 3.65
2.53 4.47 4.93
3.71 4.85 5.24
4.07 5.49 5.58
3.81 5.08 5.86
3.33 4.60 5.05
3.31 3.14
3.42 3.84
3.70 4.37
3.28 4.61
3.23 4.50
3.39
Immediate reproduction 20 set rehearsal 20 set counting 20 set counting + movement Marginal means
means
interaction was not significant (F (12,176) = 1.24, p > 0.05). A further post hoc comparison of the Condition means by the Scheffe method revealed the following: (a) the immediate reproduction condition was significantly less variable than both the 20 set rehearsal and 20 set counting conditions; and (b) the 20 set counting condition was significantly more variable than the 20 set counting + movement condition. All other single comparisons were not significant.
4. Discussion The first question of interest to be asked of the above data in terms of contrasting the models of Pepper and Herman (1970) and Laabs (1973), concerns whether CE or VE indexes decay. Pepper and Herman would predict that over an unfilled interval the trace would spontaneously decay and this would result in a negative shift in CE relative to the CE in immediate reproduction. The fact that the CEs of these two conditions in the present study (Conditions 1 and 2) were not statistically different does not support this prediction. Laabs, on the other hand, would predict that VE should differentiate an immediate repro-
R. G. Marteniuk,
G. L. Diewert /Decay
and interference
effects
221
duction condition from one where the retention interval was filled by an attention demanding mental activity (Condition 3). In this latter condition it would be expected that trace decay would occur and reproduction, since it was based ~ipon a weak or ill defined trace, would be more variable. This is in essence what occurred, and hence Laabs’ view would seem to be upheld. The second purpose of the present investigation was to determine if position cues could be retained over an unfilled retention interval. Laabs’ model predicts that these cues have access to the central processes and thus are capable of being coded and rehearsed. However since Condition 2 (unfilled 20 set retention interval) produced greater VE than Condition 1 (immediate reproduction) it would seem to contradict this prediction. This finding was unexpected since several other investigations (Posner 1967; Marteniuk and Roy 1972; Marteniuk 1973; Laabs 1973) have found that location cues were well retained over a retention interval. But a major difference between these studies and the present one was in the method of presentation of location information. In the earlier investigations, distance cues were made unreliable so S could only rely on the terminal location information for successful reproduction. The methodology of presenting movements in the present study was such so as to make both location and distance cues reliable sources of information. It may be in this case the distance information interfered with the retention of the location information. The final purpose of the present study was to contrast the views of Pepper & Herman and Laabs in terms of their predictions about interference in movement reproductions. A valid test of Pepper and Herman’s model involves comparing the CEs of Conditions 2, 3, and 4. Condition 3 involved counting backwards during the retention interval while Condition 4 involved counting and movement during the same time period. According to the model, the proprioceptive stimulation arising from these interpolated activities should have augmented the decaying memory trace and produced a CE more positive than in the comparable resting condition (in this case Condition 2). That CE failed to be differentiated among these three groups indicates a lack of support for the proposed model. One possible explanation for the null results may be derived from the methodology employed by Pepper and Herman. Their results may be unique to their experimental situation which consisted of force reproduction ranging from 1.70 to 4.25 kgms. Since there may be different retention and interference characteristics
222
R. G. Marteniuk, G. L. Diewert /Decay
and interference
effects
for force reproduction, their results may not be able to be generalized to movement reproduction. The fact that movement reproduction seems to yield different interference effects from those of force is supported by the present results, which seem to agree with Laabs’ concept of interference. In essence, the overshooting of short movements and undershooting of long movements observed in the present data is what would be expected if an adaptation level, or average movement, had been established. However, Laabs’ model would also predict that Condition 3 (counting backwards) should have produced a greater reliance on the adaptation level resulting in larger overshooting of short movements and larger undershooting of longer movements. That this did not occur detracts somewhat from the strong support previously given to Laabs’ model. From the above discussion it can be concluded that the results heavily support the view that VE is the index of trace decay in a movement reproduction task. In this respect it appears that Laabs’ concept of a decaying memory trace losing its precision and causing variability in reproduction is a viable one. Moreover, it is concluded that interference, of a proactive type, caused by the formation of an adaptation level can explain trends in CE over a range of movements S is working in. Again this is seen as support for Laabs’ model. One interesting finding of the present results, which cannot be explained by either model, is the equivalence of Conditions 1 and 4 in terms of VE. If VE is a valid measure of trace decay and counting and movement during the retention interval occupy the S’s central processing capacity there is no reason to expect the trace to be maintained to a level equal to that in immediate reproduction. Two explanations are offered for the low VE of this condition. First, the counting may not have occupied S’s attention completely and the results can be explained simply by repetition of the criterion movement during the retention interval. However, this seems unlikely since counting alone in Condition 3 produced significantly more variability when compared to Condition 1. Therefore since all Ss maintained counting while moving this explanation seems to be ruled out. The second interpretation of the above effect can be stated in terms of research by Norman (1968, 1969) who developed a memory model which states that material presented on a non-attended channel has access to short-term memory. Since the criterion trace is already
R. G. Marteniuk, G. L. Diewert /Decay
and interference
effects
223
present in short-term memory it may be that the proprioceptive feedback from the second movement, although not attended to, still gains access to memory and maintains the strength of the original trace.
References H&on, H., 1964. Adaptation level theory. New York: Harper and Row. Laabs, G. J., 1973. Retention characteristics of kinesthetic information. J. Exp. 168-177. Marteniuk, R. G., 1973. Retention characteristics of motor short-term memory Behav. 5,249-259. Marteniuk, R. G. and E. A. Roy, 1972. The codability of kinesthetic location information. Acta Psychol. 36,471-479. Norman, D. A., 1968. Toward a theory of memory and attention. Psychol. Rev. Norman, D. A., 1969. Memory while shadowing. Quart. J. Exp. Psychol. 21,85-93. Pepper, R. L. and L. M. Herman, 1970. Decay and interference effects in short-term a discrete motor act. J. Exp. Psychol. Monogr. Suppl. 83, l-18. Posner, M. L., 1967. Characteristics of visual and kinesthetic memory codes. J. 75,103-107.
Psychol.
100,
cues. J. Mot. and distance 75,522-536. retention
of
Exp. Psychol.