ICIS Conference - Brighton 2000
Sunday 14:30 to 16:20 Main Hall
Details of individual items:
Parental practices and memory in 20-month-olds
A number of general theories of cognitive development suggest the existence of links between memory in young children and parental practices (Bronfenbrenner, 1993 ; Fischer & Wozniak, 1993). Moreover, many empirical data demonstrate such links in children aged 2 to 4 years and more (Hudson, 1990 ; Fivush et al, 1988 ; Fivush et al., 1995). As a whole it was demonstrated that the form of parental talk influences the structure of children memories (the organisation and accuracy of recalled events). Authors identify several characteristics, basic to such links, which are similar to cognitive requests included in Sigel's model of distanciation (1983) : positive evaluations of the child's talk, open questions, temporal, spatial, causal and contextual perspectives on events.Factors implied in infants' memory (emotional loading, interest for the task, encoding and recall contexts, reactivations, organisation of events, recall modalities, etc.) persist beyond the second year of life. The present work aims at investigating links between maternal distanciating discourse and memory before 2 years of age.Twenty mother-infant dyads were observed when the infant was 20 months old. Memory skills were evaluated through immediate and differed imitation of sequences of action (two enabling sequences, two arbitrary sequences from Bauer, 1990). Moreover dyads were videotaped during free play centred on various toys. Maternal utterances during the interaction were coded, following Sigel, in one out of three levels of distanciation : elementary, intermediate and upper levels. Correlations between the two types of data made it possible to assess links between early memory and maternal practices encouraging children's representational skill.Two main results emerge :1. The strength of observed links depends on the quality of the representation underlying children's performances. When this representation is well organised (as in enabling sequences), performances are positively related to the frequency of utterances in the elementary and intermediate levels. On the contrary, less organised representations leads to non-significant correlations.2. In order infants Sigel observed positive correlations between representational competence and upper levels of distanciation ; on the contrary, we observe here links between the lower distanciation levels and representational competence.Results are discussed following Sigel's and Karmiloff-Smith's theories of representation.
Long term memory for images during the first 6 months of life
Margaret Cavendish, Patricia M. Riddell
While there are many studies which have used preferential lookingtechniques to examine short term memory in young infants, there is littleinformation available on the long term memory abilities of infants lessthan 6 months. Here, we report the results of a study in which mothersshowed their infants simple pictures of commonly occurring objects over aperiod of 5-6 weeks. The results suggest that even the youngest infantstested can retain information in visual memory for periods of 8-10 days.10 infants each of 2 months, 4 months and 6 months were tested. On theirfirst visit to the lab, infants were randomly divided into two groups, andeach infant was given one of two picture books to view with their motherat home. Each picture book consisted of 6 pictures giving a total of 12pictures. The picture books were designed to allow us to test the infantsusing six pairs of pictures only one of which the infant would see athome. Picture pairs were chosen to be semantically related but visuallydiscriminable (e.g. hat and coat) and were chosen to represent items thatare commonly seen by infants and are thus amongst the first to be named(Fenson et al,1994). Initial baseline preferential looking was used to test for initialpreferences for one picture in the pair over another. A computer programmewas used to time accumulated looking at the pictures. At this visit, themothers were also extensively briefed and given a training manualoutlining a programme of times and days when they should look at the bookwith their infants. Each training session at home lasted about 10 minutesand the training formed an expanding series in which the time betweenviewings was increased over a four week period (Rovee-Collier, 1995).Thus, infants saw the pictures every day for the first 7 days expandingout to once a week after 21 days. Infants had not seen the images for 5 to10 days (mean 7 days) by the time of final testing.Preferential looking was used to assess infants' recognition memory forpictures viewed with their mother. Infants were shown the picture pairs asin session one. However, now one of the pictures was familiar and theother novel. Results showed that infants of all ages were able todiscriminate the pictures viewed at home from the novel pictures. Infantsshowed a statistically significant preference for the novel pictures onretest when compared to baseline preferences. This study suggests that infants as young as 2 months are capable offorming and storing representations of simple, common images. This couldform the necessary prerequisites for early language comprehension. It isintended to test these infants for comprehension when they reach 10 monthsof age to determine whether this early visual recognition leads to earlierlanguage comprehension.
Protracting memory for an imitation task: mediated imitation and priming at 6 months
Rachel Barr, Aurora Vieira, Carolyn Rovee-Collier
Both 3- and 6-month-olds associate discrete events when they occursuccessively in close spatio-temporal contiguity (Hayne, Greco-Vigorito, &Rovee-Collier, 1993; Timmons, 1994). Timmons, for example, found that6-month-olds could associate two separate paired-associate tasks (kickingto move a mobile and starting a music box by arm waving). Three weeksafter training, when both cue-response pairs were forgotten, infants wereexposed to the music box as a reminder. When they were tested with themobile the next day they produced the response they had originallyassociated with the mobile. Because the mobile task was forgotten at thetime of reminding, reactivating the memory of the music box task must haveindirectly reactivated the memory of the mobile task as well. In the present experiment, we hypothesized that memory for ashort-lived task could be protracted if it was associated with alonger-remembered task. While 6-month-olds can remember a puppetimitation task for only 1 to 2 days, they can remember an operant traintask for 2 weeks. We now report infants memory of the imitation task canbe protracted for 2 weeks by associating it with the train task.Moreover, both memories can be recovered (reactivated) after 3 weeks. Over a 2-day training period, 6-month-olds learned to move a trainby lever pressing (Hartshorn & Rovee-Collier, 1997). Immediately afterthe second training session, an adult modeled three actions with ahand-puppet in the same context, and infants were allowed to imitate. Oneand 2 weeks later, infants who were tested with the train before they weretested with the puppet remembered the puppet task, but infants who weretested with the puppet first did not. Thus retrieving the train taskmediated retrieval of the puppet task. After a 3-week delay, infants didnot remember either the train or the puppet task. In Experiment 2, we examined whether reminding infants of one ofthe tasks would prime their memory for the other task as in Timmons(1994). Infants were trained as in Experiment 1 and allowed to forget.Twenty days later, they were given a reactivation treatment with eitherthe train or the puppet and were tested 1 day later. Reactivating thetrain restored infants memory of the puppet task and reactivating with thepuppet restored their memory of the train task. These data reveal thatexposing infants to two tasks in close temporal and spatial contiguityenabled them to be associated. By virtue of this association retrievingone memory mediated retrieval of the other after delays when it wouldotherwise be forgotten. This is the first demonstration of mediatedrecognition and priming across paradigms in infants as well as the firstto demonstrate that infants as young as 6 months can imitate a previouslymodeled action after a 2- and 3- week delay. Presumably, this mediatedretrieval occurs via a mechanism of spreading activation. These data alsorevealed a dissociation in memory performance: In the recognition task,mediation was uni-directional (train-puppet), but in the reactivationtask, it was bi-directional (train-puppet, puppet-train).References Hartshorn, K. & Rovee-Collier, C. (1997). Infant learning andlong-term memory at 6 months: A confirming analysis. DevelopmentalPsychobiology, 30, 71-85. Hayne, H., Greco-Vigorito, C., & Rovee-Collier, C. (1993).Forming contextual categories. Cognitive Development, 8, 63-82. Timmons, C. R. (1994). Associative links between discrete memoriesin early infancy. Infant Behavior and Development, 17, 431-445
Differences between deferred and elicited imitation procedures: do they matter?
Jane Herbert, Rachel Barr, Harlene Hayne
Over the past decade, two imitation procedures have been used toexamine memory development during the infancy period. In the deferredimitation procedure, an adult demonstrates unique action(s) with novelobjects and the infant's ability to reproduce those actions isassessed either immediately or after a delay. In this procedure, theadult does not verbally label the objects nor describe the actions andthe infant is not allowed to touch the objects or practice the actionsprior to the test. To assess the spontaneous production of the targetactions in the absence of an adult demonstration, independent groupsof infants are not exposed to the target actions or the objects priorto the test. In the elicited imitation procedure, an experimenteralso demonstrates unique actions with novel objects, however, thisdemonstration is accompanied by a verbal description of the objectsand actions and the infant is encouraged to practice the actions atthe end of the demonstration prior to the retention interval. Toassess the spontaneous production of target actions in the absence ofan adult demonstration, infants interact with the target objectsduring a baseline period prior to the demonstration. The duration ofthe baseline and test periods is infant-controlled. Although it isoften argued that these two imitation procedures yield comparablemeasures of memory, there has been only limited empirical researchcomparing infants' performance on both.In a series of 7 experiments, we systematically assessed the effectsof prior practice, adults' language, and choice of control procedureon both retention and generalization to novel test cues by 18- and24-month-old infants. The opportunity for prior practice did notinfluence retention when infants were tested after a short delay, butdid enhance generalization to novel test stimuli. Verbal labelling ofthe stimuli and the target actions during the demonstration and thetest, enhanced both long-term retention and generalization. The effectof verbal labelling also varied as a function of age. Finally,although the duration of the infant-controlled baseline periodcommonly used in the elicited imitation procedure was significantlyshorter than the duration of the fixed baseline period commonly usedin the deferred imitation procedure, the use of infant-controlledbaseline procedures had no effect on infants' test performance. Despite the common claim that the deferred and elicited imitationprocedures yield similar measures of memory, the results of thepresent experiments demonstrate that at least two proceduralvariations lead to systematic differences in memory performance. Based on the present findings, we conclude that prior practice andverbal labelling facilitate both the duration of retention and theflexibility of memory retrieval.
Multiple measures of memory: continuities in long-term retention?
Gabrielle F. Simcock, Harlene Hayne
Historically, there has been considerable debate about the nature ofhuman memory development. Some researchers have argued that memorydevelopment occurs in a discrete stage-like manner while others haveargued that memory development is a more smooth and continuousprocess. Data obtained using operant conditioning and deferredimitation techniques is most consistent with the view that age-relatedchanges in memory processing occur gradually between 2- and 24-monthsof age. Without exception, however, these studies have reliedexclusively on behavioral measures of memory. Whether or notdiscontinuities in memory processing begin to emerge as childrenacquire language is not known. The purpose of the present experimentwas to compare age-related changes in both behavioral and verbalrecall over delays ranging from 1 day to 1 year during a period ofrapid language acquisition. In the present experiment, 27-, 33-,and 39-month-olds participated in the same unique event on twooccasions that were separated by 24 hours. During the event, childreninteracted with a magic shrinking machine. Children were shown how tooperate the machine by lifting a lever on the front, placing a largeobject in the opening at the top, and turning a handle that produced aunique series of sounds. Following the completion of these actions,the child was shown how to open a door at the bottom of the machine toretrieve a smaller, but otherwise identical, version of the originaltoy. At each age, independent groups were tested 24 hours, 6 months,or 1 year after the target event. During the test, verbal recall,photograph recognition, and behavioral re-enactment was assessed. This test procedure combines measures of behavioral recall typicallyused with infants with verbal recall measures of memory typically usedwith older children and adults. In addition, children's receptive(PPVT III-R) and expressive (EVT) language abilities were assessed atboth the time of the event and again at the time of the test.Consistent prior studies of behavioral recall by 2- to 24-month-olds,the present study yielded age-related changes in behavioralre-enactment by 27- to 39-month-olds, particularly when the testoccurred after a long delay. Also consistent with prior studies ofbehaviour recall by 2- to 24-month-olds, the age-related changes inbehavioral re-enactment in the present study were gradual andcontinuous in nature. There were also age-related changes in verbalrecall; again, however, these changes occurred gradually between 27-and 39-months. In short, there was no evidence for an abruptstage-like change in memory processing on any memory measure. Takentogether, research from a number of different laboratories, using anumber of different experimental procedures, provides convergentevidence that age-related changes in memory processing occurthroughout the infancy period extending well into the third year oflife. Without exception, however, these changes have not beencharacterized by abrupt, qualitative shifts in memory processing. Thepresent findings add to this growing body of research and show that,even when verbal recall is assessed, memory development continues tooccur gradually. We propose that the most productive approach to thestudy of memory development will include a synthesis of findingsacross a wide range of learning and memory paradigms in an attempt touncover the large number of continuities that undoubtedly exist.
The time window: effects of reinstatement timing on retention at 3-months
Lissa Galluccio, Carolyn Rovee-Collier
Reinstatement--an abbreviated training trial--protracts retentionin animals, but few studies have examined its impact on human infantsretention. The present study examined the effect of presenting areinstatement outside of or at different points inside of the time window.A time window is the limited period after an event in which informationfrom a second event can be integrated with the first (Rovee-Collier,1995). A time window opens when the first event is over and closes whenit is forgotten. Three-month-olds typically remember the mobile task for only 5days, and a reactivation treatment on day 20 restores their retention 1day later (Hayne, 1990). In Exp. 1, therefore, we gave 3-month-olds areinstatement on day 20 and tested them 1 or 7 days later. We found thatreinstatement did not restore retention after either delay. Therefore, areinstatement given after the time window has closed does not affectretention. Experiment 2 investigated the effect of presenting a reinstatementat different points when the time window is open (0-5 days aftertraining). Previously, Adler et al. (in press) found that a reinstatementgiven on day 3, in the middle of the time window, protracted retention for14 but not 16 days since training. We replicated this procedure, testing13 days after training, and also presented a reinstatement at thebeginning of the time window (day 0) and at the end (day 5). Infantsreminded on day 0 exhibited no retention 7 days later; infants reminded onday 3 exhibited significant retention 13 days after training; and infantsgiven a reinstatement on day 5 exhibited significant retention at least 16days after training. Testing after longer delays is in progress and willcontinue until infants exhibit no retention. By October 10, the 21-daytest group will be complete. Based on previous research, we expect thatthe retention benefit of reminding late in the time window will beexponential (Rovee-Collier, Greco-Vigorito, & Hayne, 1993). In summary, at 3-months of age, giving a reinstatement outside ofthe time window is ineffective in recovering the memory, but giving thesame reinstatement within the time window produces a retention benefitthat varies with its timing. Specifically, the later its presentation,within the time window, the longer it protracts retention. Adler, S.A., Wilk, A., & Rovee-Collier, C. (in press).Reinstatement versus reactivation effects on active memory in infants.Journal of Experimental Child Psychology. Hayne, H. (1990). The effect of multiple reminders on long-termretention in human infants. Developmental Psychobiology, 23, 453-477. Rovee-Collier, C. (1995). Time windows in cognitive development.Developmental Psychology, 31, 147-169. Rovee-Collier, C., Greco-Vigorito, C., & Hayne, H. (1993). Thetime window hypothesis: Implications for categorization and memorymodification. Infant Behavior and Development, 16, 149-176.
The relative persistence of a memory after a reactivation and reinstatement at 6 months of age
Becky Sweeney, Carolyn Rovee-Collier
Memories can be maintained for long periods of time with the helpof reminders. Two types of reminders that have been used with infants andchildren are reactivation and reinstatement. A reactivation treatment is abrief exposure to an isolated component of the original training event atthe end of the retention interval. Whereas 3-month-old infants typicallyforget a mobile task 6-8 days after the original training event, infantswho receive a brief reactivation reminder 20 days after training exhibitperfect retention the next day and thereafter, forget the reactivatedmemory at the same rate they forgot the newly acquired one (Hayne, 1990).A reinstatement is an abbreviated practice trial of the original event,that alone, does not produce retention. At 3 months, reinstatementprotracts retention longer than reactivation if given when the memory isactive (Galluccio & Rovee-Collier, in press). The effect of reactivationand reinstatement on the duration of subsequent retention has not beenstudied in older infants. The present study, therefore, assessed theeffectiveness of reinstatement and reactivation in protracting theretention of a memory acquired at 6 months of age. Experiment 1 asked if the reactivated memory is forgotten at thesame rate as the newly acquired memory at 6 months. Six-month-oldstypically remember for 14 but not 21 days (Hill, Borovsky, & Rovee-Collier,1988). Infants learned to move the mobile by kicking and 20 days later,received a 2-min reactivation treatment during which the infant merelywatched as the experimenter moved the mobile at the same rate the infanthad moved it during the last 2 min of acquisition. The long-term retentiontest occurred during a nonreinforcement period 1, 3, 6, 9, 11, 13 or 14days later. Infants exhibited significant retention after all test delaysexcept 14 days. Therefore, infants forgot the reactivated and the newlyacquired memories at essentially the same rate. After just onereactivation, 6-month-old infants remembered the task for a total of 33days after training instead of only 14 days afterward. Experiment 2 assessed the effectiveness of reinstatement inprotracting retention. Infants were trained as before but received a 2-minreinstatement reminder on day 20. During reinstatement treatment, theinfants could move the mobile by kicking, as during training. Thelong-term retention test occurred 1, 14, or 28 days later. As at younger ages (Rovee-Collier, Hartshorn, & DiRubbo, 1999),reinstatement was initially ineffective unless infants recovered theoriginal learning criterion during the 2-min reminder procedure. Timingreinstatement from the first kick, however, alleviated this problem.Infants exhibited significant retention after all test delays but could notbe tested after longer delays because they outgrew the task. The resultsof these experiments show that reactivation and reinstatement treatmentsare both effective in protracting memory at 6-months, but the reinstatementtreatment protracts retention at least twice as long. These results havebeen replicated with the train task.
Reinstatement vs. reactivation effects on active memory in infants
Amy Wilk, S.A. Adler, Carolyn Rovee-Collier
Campbell and Jaynes (1966) defined reinstatement as a periodic andpartial repetition of the original event throughout the retention interval,whereas Spear and Parsons (1976) defined reactivation as a singlepresentation of an isolated component of the event at the end of theretention interval. Despite the fact that these reminder paradigms areprocedurally quite different, both protract retention so that it isexhibited after delays not otherwise possible, and most developmentalpsychologists do not distinguish between them. In two recent studies,presenting a single reinstatement at the end of a 3-week retentioninterval, when the memory was inactive, did not alleviate the forgetting ofeither 2-month-olds (Rovee-Collier, Hartshorn, & DiRubbo, 1999) or3-month-old infants (Galluccio & Rovee-Collier, in press), whereaspresenting a single reactivation reminder after the same delay did. Theseresults led us to question whether these two reminder procedures truly arefunctionally equivalent. Presently, 102 3-month-old infants learned tokick to move an overhead mobile via a ribbon connected to the infantsankle. Independent groups of infants received a 3-min reminder--eitherreactivation or reinstatement--3 days after training, when the memory isstill active, but its specific details have been forgotten. During thereinstatement reminder, movement of the mobile was contingent on theinfants kicks, while during a reactivation reminder, the experimenter movedthe mobile noncontingently. In Experiment 1, we measured retention after increasing delaysuntil infants forgot the task altogether. A single reinstatementprotracted retention for 2 weeks since training, whereas a singlereactivation protracted retention for only 1 week. Controls who wereovertrained or exposed for the same amount of time immediately aftertraining exhibited no retention even 1 week later. Because the reminderwas presented at a time when the specific details of the training mobilehad been forgotten, we speculated that a novel mobile might also beeffective in protracting the memory. We found that reactivation with anovel mobile also prolongs the memory for 1 week after training (Exp. 2),but during reinstatement, only the original training mobile prolonged thememory for 2 weeks after training (Exp. 3). Reinstatement reminders alsoaffect the specificity of the memory, apparently resetting the memory sothat infants initially remembered its specific details and then laterforgot them again (Exp. 4). These data demonstrate that the distinctionbetween reinstatement and reactivation is not artificial. In addition todiffering procedurally, reinstatement and reactivation differ functionally,with different memory-preserving effects.
Developmental changes in forgetting of reactivated memories over the first year of life
Karen Hildreth, Carolyn Rovee-Collier
Over the first year of life, infants of all ages forget more andmore gradually (Hartshorn et al., 1998). Once their memories areforgotten, however, they can be reactivated if infants are merely exposedto a retrieval cue that is presented in advance of the retention test. Thisreminder treatment (reactivation) has been used with preverbal younginfants who had learned to move a mobile by kicking. All infants receivedthe reactivation treatment 1 week after forgetting the mobile task (3months, 14 days after training; 6 months; 20 days after training) and werethen tested for retention after a series of delays. These studies revealedthat at both ages, the reactivated memory was forgotten at the same rate asthe newly acquired memory (Rovee-Collier et al., 1980; Sweeney &Rovee-Collier, 1999). In the present study, we examined the forgetting of a reactivatedmemory at 6, 9, and 12 months of age using a train task which was developedas an upward extension of the mobile task. In this task, infants learn topress a lever to move a miniature train around a circular track. This taskyields the same parameters of retention at 6 months as the mobile task(Hartshorn & Rovee-Collier, 1997). All infants were recruited from birthannouncements and randomly assigned to experimental conditions. One weekafter forgetting the task, 6-, 9-, and 12-month-olds received areactivation treatment (i.e., 20, 49, and 63 days after training,respectively). This treatment consisted of a 2-min period during whichinfants were passively exposed to the train moving at an identical rate tothe rate seen during the final minutes of acquisition. Independent groupswere tested for retention 6, 9, 14, or 21 days after reactivation at 6months, 3, 6, 14, 28, 35, or 42 days after reactivation at 9 months, and14, 28, 42, 49, or 56 days after reactivation at 12 months. Overall, infants take longer to forget initially and to reforgetafter priming (reminding) with age. Moreover the reactivated memory isforgotten at approximately the same rate as the original memory. Infantstrained at 6 months remembered both the newly acquired memory and thereactivated memory for 14 but not 21 days. Infants trained at 9 monthsremembered the newly acquired memory for 42 days and the reactivated memoryfor 28 but not 42 days; and infants trained at 12 months remembered thenewly acquired memory for 56 days and the reactivated memory for 42 but not56 days. Testing 35 days at 9 months and 49 days at 12 months is currentlyin progress. The current data reveal that another temporal parameter of memorychanges progressively over the first year of life. Previously, wedemonstrated that the duration of retention increases linearly (Hartshorn,et al., 1998) and the latency of priming decreases linearly (Hildreth &Rovee-Collier, in press) between 3 and 12 months of age. Becauseincreasingly older infants remember newly acquired memories increasinglylonger, recover them more rapidly after priming, and then reforget themmore slowly, the net effect of a single reminder is to make memories atolder ages accessible for increasingly longer periods. Including theinterval between forgetting and reminding, this study reveals that a singlereactivation treatment approximately doubles the life of a memory over thefirst year of life.
An exploration of infant working memory
Kevin A. Pelphrey, J. Steven Reznick, Barbara D. Goldman, Judy Morrow, N. Sasson
Abstract: Working memory (WM) allows infants to escape from a simpleworldview and embrace a more sophisticated perspective that includesthe past and the future. Nonetheless, we know surprisingly littleabout the early development of WM. Research indicates significant WMability in the human infant late in the first year, but the proceduresthat have been employed are less than optimal. Moreover, the primaryparameter of WM in adults is the amount of information that can bestored, but procedures for assessing WM in infants have focused almostexclusively on the duration of storage. We attempted to fill thesegaps by exploring infant WM using a more optimal procedure (a'windows and curtains' task), a definition of WM capacity thatcaptures amount and duration of storage, and an age-range that seemsappropriate for detecting the emergence of WM. We have tested 11 healthy, full term, male and female 4-12-month oldinfants to date (mean age 3D 9.64 months, range 3D 7.46 to 12.33months). Nine of the infants were male and two were female.Each infant sat on his parent's lap facing a projection screen and aneye-imaging system. Parents sat on a swivel chair and watched a smallvideo monitor that provided them with a video image of their infant'sface. The parents were instructed to position the infant's body sothat the infant's eyes remained in view. Parents were signaled toturn to the rear of the room or to face the projection screen. Allinfants received 12 counterbalanced trials, reflecting sixconditions. As illustrated in Table 1, the conditions were formed asa function of the number of possible locations, the number ofto-be-remembered objects, and the delay interval. The order ofconditions was counterbalanced across trials.At the start of each trial, 2 or 4 computer-generated 'curtains' wereraised simultaneously revealing 2 or 4 windows. A five-second digitalvideo of a smiling face (and voice) of 1 or 2 female volunteersappeared in 1 or 2 of the windows. The active windows werecounterbalanced across conditions. After the stimulus presentation,the window went blank, the curtains were lowered simultaneously, andthe parent was told to rotate such that she and her infant faced theback of the room. After 5 or 10 seconds, the parent was signaled toswivel and face the projection screen. The curtains were raised, andthe remote eye-imaging system recorded the infant's eye movements. Post-experimental processing revealed the location of first gaze andlongest gaze, but only first gaze is reported here. A trial wasconsidered correct if the infant gazed first to the location where aface had appeared.We calculated the percentage of trials on which the infant respondedwith a correct gaze within each condition. As revealed in Table 2,infants performed better on trials involving a 5-sec delay versus a10-sec delay. Infants performed considerably better on trialsinvolving 2 potential hiding locations versus 4 locations. Finally,infants were well above chance levels in the conditions involving 1to-be-remembered stimulus, while performing only marginally abovechance on the trials involving 2 hidden stimuli.09These results suggest some utility in a computer-generated windows andcurtains procedure and the use of multiple definitions of WM capacity.Table 1.Design of Conditions Condition # of Locations #of Hidden People Delay IntervalOne 2 1 05 secondsTwo 2 1 10 secondsThree 4 1 05 secondsFour 4 1 10 secondsFive 4 2 05 secondsSix 4 2 10 secondsTable 2.Percentages Correct by Type of TrialsCondition Mean SEM1. All 5 second trials 74.24 6.092. All 10 second trials 60.61 6.063. All 2 location - 1 hidden person trials 79.54 6.584. All 4 location - 1 hidden person trials 54.54 8.135. All 4 locations - 1 hidden person trials 54.54 8.136. All 4 locations - 2 hidden person trials 68.18 7.60