Forgetting of recently acquired or recently reactivated memories

Four experiments compared the rates of forgetting following acquisition of a conditioned aversion and following a reactivation treatment given long after conditioning had been completed. The “reactivation treatment” consisted of a single presentation of the unconditioned stimulus, a procedure known to reinstate, following substantial forgetting, the behavior seen immediately after conditioning. It was first determined that the decrement in performance 1, 3, or 7 days later tended to be more rapid just after original conditioning than following a reactivation treatment given 27 days after conditioning. Subsequent experiments confirmed that the forgetting seen 3 or 7 days after original conditioning was in fact greater than forgetting 3 or 7 days after the reactivation treatment that had followed conditioning by 27 days; also, tests permitted rejection of the hypothesis that this effect could be attributed to nonassociative (systemic) consequences of the conditioning situation. Finally, tests indicated that retention 24 hr after a reactivation treatment was significantly better if the reactivation treatment followed conditioning by 27 days than if it were given just 3 min or 24 hr after conditioning. The central observation emerging from this study, that forgetting is more rapid following original learning than following a temporally remote reactivation treatment, was discussed in terms of potential interactions between the age (or accessibility) of a memory and processes that might be instigated by a reactivation treatment.     

Increased susceptibility of aphasics to a distractor task in the recall of verbal commands

The ability of 15 control, 15 nonaphasic brain-damaged, and 15 aphasic patients to carry out three-word commands on the Token Test was studied under three conditions: no delay, 20-sec unfilled delay, and 20-sec delay filled with a counting task. Only aphasics with mild to moderate comprehension deficit participated in the experiment and their scores in the no-delay condition were not inferior to those of the other two groups. The 20-sec unfilled delay did not bring about a decrement of the performance in any group, while all of them were impaired with 20-sec filled delay. The rate of forgetting was, however, significantly greater in aphasics than in patients without language disorders, even when the scores of the no-delay condition were introduced as covariates in the analysis of the filled-delay condition. The same result was obtained when, in a second experiment, 4 sec elapsed between the end of the command and the beginning of the counting activity. The increased susceptibility of aphasics to the disruptive effect of the distractor task is viewed as following a failure in organizing verbal information, a deficit that may contribute to lowering their comprehension level.     

Differential effectiveness of various prior-cuing treatments in the reactivation and maintenance of memory

In 3 experiments, changes were examined in the characteristics of newly acquired and reinstated memories over time in preweanling rats. Experiment 1 indicated that forgetting after conditioning was monotonic, with the upper limit of retention at approximately 120 min posttraining. In Experiment 2, Ss were exposed to various elements of the training episode before testing, after either a 3- or a 24-hr retention interval. The results indicated that the prior-cuing treatments were differentially effective and that the effectiveness of a reactivation treatment may change as a function of the retention interval. Experiment 3 indicated that Ss expressed a conditioned aversion at much longer intervals following reactivation treatments than after initial conditioning. Furthermore the susceptibility of the reinstated memory to forgetting was dependent on the prior-cuing treatment used. The results suggest a change in the memorial representation of the conditioning episode over time.     

Alleviation of forgetting of discrimination learning

Reactivation treatments intended to alleviate forgetting in rats were tested in two discrimination tasks—instrumental learning with brightness or with spatial location as the discriminanda. For memories acquired 28 days earlier, forgetting was alleviated with both tasks when testing was preceded by certain reactivation treatments. Therefore, the generality of the effectiveness of reactivation treatments for alleviating forgetting is extended to include discrimination learning and response measures other than go, no-go behavior.     

The spacing effect: Additions to the theoretical and empirical puzzles

Four studies examined the MP-DP effect (spacing effect) in four quite different situations: recognition of letters, verbal discrimination, short free recall lists, and recall of MP items presented twice, with an intervening interval inserted to produce forgetting. MP-DP differences were found in all studies. Of particular interest were three interactions. Subjects with a low criterion of responding in the letter study lost the MP-DP effect over a 30-sec delay, and subjects with a high criterion did not. A clear MP-DP effect, but no lag effect, was found only with unmixed verbal discrimination lists. In free recall, a sharp lag effect was shown for words presented three times but not for words presented twice. A forgetting interval inserted between the two occurrences of an MP item did not appreciably aid its recall. The results were found to pose severe problems for current theoretical ideas about the spacing effect.     

Children's reactions to failure as a function of interresponse interval

Several studies have reported that nonreward facilitates subsequent performance; other studies have found that failure is followed by a performance decrement. Experiments that have shown facilitating effects of nonreward have used interresponse intervals of at least 5 sec, whereas those that have shown decremental effects of failure have used 0-sec interresponse intervals. The present study examined the effects of .5-, 1.0- and 5.0-sec interresponse intervals on children's lever-pulling responses following success and failure on a ball tower task. Second- and third-grade children responded slower following failure relative to success with .5- and 1.0-sec interresponse intervals. Speeds following success and failure did not differ when the interresponse interval was 5.0 sec. Increases in interresponse interval were associated with increases in speeds following failure, but speeds following success were not related to interresponse interval. These results were discussed in terms of frustration-produced competing responses and Elliott (1970) analysis of the influence of preparatory intervals on children's reaction-time performance.     

Very rapid forgetting: Reply to Muter

We reply to the commentary in which Muter (1995) disputes the findings and arguments of Cunningham, Healy, Till, Fendrich, and Dimitry (1993) concerning the rate of forgetting from primary memory. Although Muter (1980) had reported very rapid forgetting when secondary memory processes were minimized, Cunningham et al. found that the rate of forgetting from primary memory was no more rapid when secondary memory processes were minimal than it was when secondary memory processes were substantial. We locate the discrepancy between the two studies specifically at recall performance on the 0-sec retention interval, and we argue that the very rapid forgetting found by Muter (1980) can be attributed in large part to the fact that although subjects in his experiments did not expect to recall the letters after a filled retention interval, at the time of encoding and after an unfilled delay they did have a high overall expectancy to recall the letters.     

The Effects of Practice Trials and Prior Learning on Motor Memory

The effects of prior positions (PL), practice reinforcements of the criterion distance (CT), and retention intervals on proactive interference (PI) in a 20-cm. linear positioning task were examined. Independent treatment groups had either 0, 3, or 5 PL, with 1, 3, or 10 CT, and a 5-, 15-, or 50-sec. retention interval. Only absolute error scores at recall indicated PI. This forgetting occurred only under the highly restricted conditions of 5 PL and 1 CT after 15-and 50-sec. retention intervals. Since 0 PL groups showed no differences in recall over levels of retention intervals, PI alone apparently caused the forgetting.     

Reliability of electrodermal habituation measures under two conditions of stimulus intensity

The present study investigated test-retest reliability of habituation of the evoked skin conductance response. Subjects received 20 presentations of a 1000-Hz, 3-sec tone at the same time of day on two separate occasions, separated by an interval of 97–160 days. Thirteen subjects received stimuli of 90 dB, while for 24 subjects, stimulus intensity was 70 dB. Interstimulus interval was 21 sec for both groups. Both absolute rate of habituation and trials to criterion displayed moderate reliability, and the relationships between habituation measures and other aspects of electrodermal activity were in agreement with previous findings.     

Ontogeny of early event memory: I. Forgetting and retrieval by 2- and 3-month-olds

In 2 experiments, 2-month-olds, trained in the mobile conjugate reinforcement paradigm for two daily sessions, showed retrieval deficits relative to 3-month-olds. In Experiment 1, tests of simple forgetting administered to 2-month-olds after retention intervals of 1, 3, 6, and 9 days (a period over which 3-month-olds remember the contingency) indicated that their forgetting was complete after delays greater than 1 day. In Experiment 2, reactivation treatments administered to 2- and 3-month-olds alleviated forgetting after a retention interval of 28, but not 35, days in the 3-month-old group only. Previously, alleviated forgetting by a reactivation treatment had been demonstrated in 2-month-olds after a delay of 18 days. In both of the present experiments, performance of the two age groups did not differ during the immediate retention test at the end of training. These results suggest that neither the age of the infant nor the age of the memory determines memory retrieval after long delays; instead, it appears to be determined by the length of time that a memory has been inaccessible (i.e., forgotten). We propose that factors which delay simple forgetting will correspondingly increase the length of the interval over which a retrieval cue can still be effective in a reactivation paradigm, irrespective of the age of the infant or the age of the memory.     

Effects of encoding strategy,presentation modality,and scoring method on STM performance with the Peterson and Peterson technique

The Peterson and Peterson (1959) STM experiment was replicated with variation of presentation modality and encoding strategy. The effect of various scoring criteria was also analyzed. The recall data showed that a Peterson and Peterson type forgetting curve was obtained using auditory presentation and instructions to rehearse vocally the trigrams when scoring only completely correct recall within the first 3 sec of the recall interval. With visual presentation and instructions to find meaningful trigram interpretations, the forgetting curve was higher and much more flat, especially when scoring position correct recall within the total 0-10-sec recall interval. In a buildup of PI experiment, no buildup of PI could be detected when visual presentation was used together with instructions to find meaningful trigram interpretations. The importance of the different encoding activities for recall performance was discussed.     

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).     

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.     

Intertrial intervals and visual habituation in neonates

Eighteen 3-day-old human neonates were shown a 12 by 12 black-white checkerboard target for 45-sec. trials with either a 10-, 20-, or 30-sec. intertrial interval until their visual fixation time decreased to a set criterion for habituation. On subsequent recovery trials, a 2 by 2 black-white checkerboard target received significantly longer fixations from boys in the 10-sec. and girls in the 20-sec. conditions. 30-sec. intervals, however, produced little habituation and recovery. The implications of these findings are discussed.     

Short-term temporal changes in free recall

An experimental study of short-term memory for lists of familiar English words is reported. Lists of 10, 20, and 30 unrelated words were presented at a 1-sec. rate. Retention was measured by free recall after intervals of 0, 15 and 30 sec. A counting task was used to prevent rehearsal during the retention interval. The absolute level of recall increased with length of list whereas the percentages retained showed the reverse trend. The recall scores decreased steadily as a function of retention interval, with the rates of forgetting comparable for the three lengths of list. The decline in the amount recalled was due in large measure to the loss of the terminal items in the list. Consequently, the pronounced recency effect present on the immediate test of recall was progressively reduced as a function of time. By contrast retention of the initial part of the list was relatively stable. These variations in rate of forgetting are attributed to differences among serial positions in susceptibility to proactive inhibition.     

Heart rate conditioning in young infants using a visual conditional stimulus

Trace heart rate conditioning was evaluated in 16 infants having a mean age of 4.5 months. The Experimental Group received a 3-sec blinking light pattern as the CS, followed by a 3-sec interstimulus interval (ISI), and 3-sec tone as the UCS. The Control Group received an equal number of presentations of the CS and UCS at randomized intervals and in a randomized order. The acquisition of a conditioned deceleration during the period which included the visual CS and the ISI was demonstrated only in the Experimental males. Response differences were also found in the absence of the auditory UCS, with only Experimental females exhibiting a deceleration.     

Fixed-interval behavior maintained by conditioned reinforcement

The key-pecking of a pigeon was reinforced with grain on an 18-min second-order schedule. During the 18 min, a key peck which completed a 3-min fixed interval produced a stimulus of 0.5-sec duration. The first 3-min fixed interval completed after 18 min resulted in primary reinforcement. Behavior characteristic of fixed-interval schedules was produced on both the 3-min components and the 18-min schedule. This performance was shown to be enhanced whenever the 0.5-sec stimulus was also presented before the presentation of grain.     

Dual effects of response blocking following avoidance learning

It was shown that either enhanced or decreased avoidance responding by rats could be produced by the same response blocking procedure occurring after avoidance training. The particular result produced depended on (1) the duration of the blocking trial and (2) when during the retention interval the blocking trial occurred. Results were interpreted in terms of a memory reactivation explanation and implications for the therapeutic uses of extinction were discussed.     

An empirical note on the role of verbal labels in motor short-term memory tasks

Previous studies of motor short-term memory have shown that when a criterion movement on a semicircular positioning task is accompanied by an appropriate verbal label (a clock-face position), recall of the movement is more accurate than when only the movement is presented. This increased accuracy could be due to either the additional spatial information provided by the label or enhanced retention of the movement information. These two alternatives cannot be distinguished on the basis of previous studies because the studies have not evaluated movement accuracy following presentation of the label alone. The present study employed such a condition in addition to the movement-only and movement-plus-label conditions to distinguish between the two hypotheses. In all conditions, subjects were asked to move to the criterion position after a retention interval of either 5 sec or 60 sec. Evidence indicated that subjects who received both the label and the movement tended to use the spatial information provided by the label at the 60-sec interval. The evidence did not indicate that the verbal label actually enhanced retention of the movement information.     

An Empirical Note on the Role of Verbal Labels in Motor Short-Term Memory Tasks

Previous studies of motor short-term memory have shown that when a criterion movement on a semicircular positioning task is accompanied by an appropriate verbal label (a clock-face position), recall of the movement is more accurate than when only the movement is presented. This increased accuracy could be due to either the additional spatial information provided by the label or enhanced retention of the movement information. These two alternatives cannot be distinguished on the basis of previous studies because the studies have not evaluated movement accuracy following presentation of the label alone. The present study employed such a condition in addition to the movement-only and movement-plus-label conditions to distinguish between the two hypotheses. In all conditions, subjects were asked to move to the criterion position after a retention interval of either 5 sec or 60 sec. Evidence indicated that subjects who received both the label and the movement tended to use the spatial information provided by the label at the 60-sec interval. The evidence did not indicate that the verbal label actually enhanced retention of the movement information.