Long-term retention in 3.5-month-olds: familiarization time and individual differences in attentional style

Examining infants' visual paired comparison performance in the US and rural Malawi

Measures of attention and memory were evaluated in 6- to 9-month-old infants from two diverse contexts. One sample consisted of African infants residing in rural Malawi (N = 228, 118 girls, 110 boys). The other sample consisted of racially diverse infants residing in suburban California (N = 48, 24 girls, 24 boys). Infants were tested in an eye-tracking version of the visual paired comparison procedure and were shown racially familiar faces. The eye tracking data were parsed into individual looks, revealing that both groups of infants showed significant memory performance. However, how a look was operationally defined impacted some-but not other-measures of infant VPC performance. RESEARCH HIGHLIGHTS: In both the US and Malawi, 6- to 9-month-old infants showed evidence of memory for faces they had previously viewed during a familiarization period. Infant age was associated with peak look duration and memory performance in both contexts. Different operational definitions of a look yielded consistent findings for peak look duration and novelty preference scores-but not shift rate. Operationalization of look-defined measures is an important consideration for studies of infants in different cultural contexts.

Real-world statistics at two timescales and a mechanism for infant learning of object names

Infants begin learning the visual referents of nouns before their first birthday. Despite considerable empirical and theoretical effort, little is known about the statistics of the experiences that enable infants to break into object–name learning. We used wearable sensors to collect infant experiences of visual objects and their heard names for 40 early-learned categories. The analyzed data were from one context that occurs multiple times a day and includes objects with early-learned names: mealtime. The statistics reveal two distinct timescales of experience. At the timescale of many mealtime episodes (n = 87), the visual categories were pervasively present, but naming of the objects in each of those categories was very rare. At the timescale of single mealtime episodes, names and referents did cooccur, but each name–referent pair appeared in very few of the mealtime episodes. The statistics are consistent with incremental learning of visual categories across many episodes and the rapid learning of name–object mappings within individual episodes. The two timescales are also consistent with a known cortical learning mechanism for one-episode learning of associations: new information, the heard name, is incorporated into well-established memories, the seen object category, when the new information cooccurs with the reactivation of that slowly established memory.

Entwicklung des Gedächtnisses bei präverbalen Kindern

Zusammenfassung. Gedächtnis ist eine elementare Fähigkeit, deren Entwicklungsverlauf insbesondere für das präverbale Alter bisher nicht eindeutig beschrieben ist. Zur Erfassung von Gedächtnisleistungen im präverbalen Alter werden verschiedene Verhaltensmaße herangezogen. Früheste Beobachtungen von Leistungen des impliziten Gedächtnisses sind über Präferenzverhalten in Paarvergleichs- und Habituationsaufgaben möglich und basieren auf einem Reizinformationsvergleich. Auch operant konditioniertes Verhalten in der Mobile- und Zug-Aufgabe indiziert eine implizite Gedächtnisleistung und basiert auf dem Lernen aus Konsequenzen. Imitationsverhalten als Leistung des expliziten Gedächtnissystems beruht auf Modelllernen in Aufgaben zur verzögerten Imitation. Sowohl im impliziten als auch im expliziten System sind im Entwicklungsverlauf Zuwächse der Gedächtnisleistungen hinsichtlich Kapazität, Behaltensdauer, Enkodiergeschwindigkeit und Flexibilität im Abruf beobachtbar. Die den Aufgaben zur Erfassung von Gedächtnisleistungen zugrundeliegenden Mechanismen deuten auf eine sukzessive Entwicklung zuerst des impliziten, dann des expliziten Systems hin.

Visual attention to meaningful stimuli by 1- to 3-year olds: implications for the measurement of memory

The visual recognition memory (VRM) paradigm has been widely used to measure memory during infancy and early childhood; it has also been used to study memory in human and nonhuman adults. Typically, participants are familiarized with stimuli that have no special significance to them. Under these conditions, greater attention to the novel stimulus during the test (i.e., novelty preference) is used as the primary index of memory. Here, we took a novel approach to the VRM paradigm and tested 1-, 2-, and 3-year olds using photos of meaningful stimuli that were drawn from the participants' own environment (e.g., photos of their mother, father, siblings, house). We also compared their performance to that of participants of the same age who were tested in an explicit pointing version of the VRM task. Two- and 3-year olds exhibited a strong familiarity preference for some, but not all, of the meaningful stimuli; 1-year olds did not. At no age did participants exhibit the kind of novelty preference that is commonly used to define memory in the VRM task. Furthermore, when compared to pointing, looking measures provided a rough approximation of recognition memory, but in some instances, the looking measure underestimated retention. The use of meaningful stimuli raise important questions about the way in which visual attention is interpreted in the VRM paradigm, and may provide new opportunities to measure memory during infancy and early childhood.

Toddlers' bias to look at average versus obese figures relates to maternal anti-fat prejudice

Anti-fat prejudice (weight bias, obesity stigma) is strong, prevalent, and increasing in adults and is associated with negative outcomes for those with obesity. However, it is unknown how early in life this prejudice forms and the reasons for its development. We examined whether infants and toddlers might display an anti-fat bias and, if so, whether it was influenced by maternal anti-fat attitudes through a process of social learning. Mother-child dyads (N=70) split into four age groups participated in a preferential looking paradigm whereby children were presented with 10 pairs of average and obese human figures in random order, and their viewing times (preferential looking) for the figures were measured. Mothers' anti-fat prejudice and education were measured along with mothers' and fathers' body mass index (BMI) and children's television viewing time. We found that older infants (M=11months) had a bias for looking at the obese figures, whereas older toddlers (M=32months) instead preferred looking at the average-sized figures. Furthermore, older toddlers' preferential looking was correlated significantly with maternal anti-fat attitudes. Parental BMI, education, and children's television viewing time were unrelated to preferential looking. Looking times might signal a precursor to explicit fat prejudice socialized via maternal anti-fat attitudes.

Eighteen-month-olds' memory for short movies of simple stories

This study investigated twenty four 18-month-olds' memory for dynamic visual stimuli. During the first visit participants saw one of two brief movies (30 seconds) with a simple storyline displayed in four iterations. After 2 weeks, memory was tested in the visual paired comparison paradigm in which the familiar and the novel movie were contrasted simultaneously and displayed in two iterations for a total of 60 seconds. Eye-tracking revealed that participants fixated the familiar movie significantly more than the novel movie, thus indicating memory for the familiar movie. Furthermore, time-dependent analysis of the data revealed that individual differences in the looking-patterns for the first and second iteration of the movies were related to individual differences in productive vocabulary. We suggest that infants' vocabulary may be indicative of their ability to understand and remember the storyline of the movies, thereby affecting their subsequent memory.

The effects of exposure to dynamic expressions of affect on 5-month-olds' memory

The purpose of this study was to examine the behavioral effects of adults' communicated affect on 5-month-olds' visual recognition memory. Five-month-olds were exposed to a dynamic and bimodal happy, angry, or neutral affective (face-voice) expression while familiarized to a novel geometric image. After familiarization to the geometric image and exposure to the affective expression, 5-month-olds received either a 5-min or 1-day retention interval. Following the 5-min retention interval, infants exposed to the happy affective expressions showed a reliable preference for a novel geometric image compared to the recently familiarized image. Infants exposed to the neutral or angry affective expression failed to show a reliable preference following a 5-min delay. Following the 1-day retention interval, however, infants exposed to the neutral expression showed a reliable preference for the novel geometric image. These results are the first to demonstrate that 5-month-olds' visual recognition memory is affected by the presentation of affective information at the time of encoding.

Three-year-olds' memory for a person met only once at the age of 12 months: very long-term memory revealed by a late-manifesting novelty preference

This study examined three-year-olds' verbal and non-verbal memory for a person met only once after a 28 month interval. Children in the Test group (N=50) had participated in an earlier experiment at our lab at the age of 12 months where they met one of two possible experimenters. At this past event half of the children were tested by one, the other half by the other experimenter. At the follow-up, run by a naïve experimenter, the children were shown two videos from the original experiment in a visual paired comparison task: One with the specific experimenter testing them at the original visit (the Target) and one of the other experimenter (the Foil), with whom they had no experience. When explicitly asked, the children's responses did not differ from chance. However, eye-tracking data revealed a late-manifesting novelty preference for the "Foil" person indicating memory for the "Target" person met once before.

Visual short-term memory for complex objects in 6- and 8-month-old infants

Infants' visual short-term memory (VSTM) for simple objects undergoes dramatic development: Six-month-old infants can store in VSTM information about only a simple object presented in isolation, whereas 8-month-old infants can store information about simple objects presented in multiple-item arrays. This study extended this work to examine the development of infants' VSTM for complex objects during this same period (N = 105). Using the simultaneous streams change detection paradigm, Experiment 1 confirmed the previous developmental trajectory between 6 and 8 months. Experiment 2 showed that doubling the exposure time did not enhance 6-month-old infants' change detection, demonstrating that the developmental change is not due to encoding speed. Thus, VSTM for simple and complex objects appears to follow the same developmental trajectory.

Infants' Visual Recognition Memory for a Series of Categorically Related Items

We examined the interactions between visual recognition memory, working memory, and categorization by examining 6-month-old infants' (N = 168) memory for individual items in a categorized list (e.g., images of dogs or cats). In Experiments 1 and 2, infants were familiarized with 6 different cats or dogs, presented one at a time on a series of 15-s familiarization trials. When the test occurred immediately after the sixth familiarization trial (Experiment 1), infants showed strong novelty preference for items presented on the fourth or fifth familiarization trial, but not for the items presented on the first three trials or on the sixth trial. When a brief (15-s) retention delay occurred between the end of the sixth trial and the test trials (Experiment 2), memory for the sixth item was enhanced, memory for the fourth item was impaired, and memory for the fifth was unchanged relative to when no retention delay was included. Experiment 3 confirmed that infants can form a memory for the first item presented. These results reveal how factors such as interference and time to consolidate influence infants' visual recognition memory as they categorize a series of items.

Infant categorization of path relations during dynamic events

Fundamental to amassing a lexicon of relational terms (i.e., verbs, prepositions) is the ability to abstract and categorize spatial relations such as a figure (e.g., boy) moving along a path (e.g., around the barn). Three studies examine how infants learn to categorize path over changes in manner, or how an action is performed (e.g., running vs. crawling). Experiment 1 (n = 60) finds that 10- to 12-month-old English-learning infants categorize a figure's path. In Experiment 2 (n = 27) categorization is disrupted when the ground object is removed, suggesting the relation between figure and ground defines the path. Experiment 3 (n = 24) shows that language may be a mechanism guiding category formation. These studies suggest that English-learning infants can categorize path, a component lexicalized in the world's languages.

The comparator model of infant visual habituation and dishabituation: recent insights

Current knowledge of the perceptual and cognitive abilities in infancy is largely based on the visual habituation-dishabituation method. According to the comparator model [e.g., Sokolov (1963a) Perception and the conditioned reflex. Oxford: Pergamon Press], habituation refers to stimulus encoding and dishabituation refers to discriminatory memory performance. The review also describes the dual-process theory and the attention disengagement approach. The dual-process theory points to the impact of natural stimulus preferences on habituation-dishabituation processes. The attention disengagement approach emphasizes the contribution of the ability to shift the attention away from a stimulus. Moreover, arguments for the cognitive interpretation of visual habituation and dishabituations are discussed. These arguments are provided by physiological studies and by research on interindividual differences. Overall, the review shows that current research supports the comparator model. It emphasizes that the investigation of habituation and dishabituation expands our understanding of visual attention processes in infants.

Visual recognition memory across contexts

In two experiments, we investigated the development of representational flexibility in visual recognition memory during infancy using the Visual Paired Comparison (VPC) task. In Experiment 1, 6- and 9-month-old infants exhibited recognition when familiarization and test occurred in the same room, but showed no evidence of recognition when familiarization and test occurred in different rooms. In contrast, 12- and 18-month-old infants exhibited recognition irrespective of testing room. Thus, flexibility across a change of room was observed at a younger age than flexibility across a change of background that has previously been seen with the VPC procedure (Robinson & Pascalis, 2004). To determine if limitations in representational flexibility across a change of background could be overcome by experiences during encoding, in Experiment 2, 6-, 9-, 12- and 18-month-old infants were familiarized with a picture on multiple backgrounds. At all ages, infants showed recognition across a change in background at test. These findings indicate that dissociating an item from its context during encoding may be an important factor in understanding the representational flexibility of visual recognition memory in infancy. Developmental changes in representational flexibility are likely driven by changes in the functional maturity of the hippocampal formation, and experience.

Stable individual differences in number discrimination in infancy

Previous studies have shown that as a group 6-month-old infants successfully discriminate numerical changes when the values differ by at least a 1:2 ratio but fail at a 2:3 ratio (e.g. 8 vs. 16 but not 8 vs. 12). However, no studies have yet examined individual differences in number discrimination in infancy. Using a novel numerical change detection paradigm, we present more direct evidence that infants' numerical perception is ratio-dependent even within the range of discriminable ratios and thus adheres to Weber's Law. Furthermore, we show that infants' numerical discrimination at 6 months reliably predicts their numerical discrimination abilities but not visual short-term memory at 9 months. Thus, individual differences in numerical discrimination acuity may be stable within the first year of life and provide important avenues for future longitudinal research exploring the relationship between infant numerical discrimination and later developing math achievement.

Infant attention and visual preferences: converging evidence from behavior, event-related potentials, and cortical source localization

In this study, we had 3 major goals. The 1st goal was to establish a link between behavioral and event-related potential (ERP) measures of infant attention and recognition memory. To assess the distribution of infant visual preferences throughout ERP testing, we designed a new experimental procedure that embeds a behavioral measure (paired comparison trials) in the modified-oddball ERP procedure. The 2nd goal was to measure infant ERPs during the paired comparison trials. Independent component analysis (ICA) was used to identify and to remove eye-movement components from the electroencephalographic data, thus allowing for the analysis of ERP components during paired comparison trials. The 3rd goal was to localize the cortical sources of infant visual preferences. Equivalent current dipole analysis was performed on the ICA components related to experimental events. Infants who demonstrated novelty preferences in paired comparison trials demonstrated greater amplitude Negative central ERP components across tasks than infants who did not demonstrate novelty preferences. Visual preference also interacted with attention and stimulus type. The cortical sources of infant visual preferences were localized to inferior and superior prefrontal cortex and to the anterior cingulate cortex.

The effects of intersensory redundancy on attention and memory: infants' long-term memory for orientation in audiovisual events

This research examined the effects of bimodal audiovisual and unimodal visual stimulation on infants' memory for the visual orientation of a moving toy hammer following a 5-min, 2-week, or 1-month retention interval. According to the intersensory redundancy hypothesis (L. E. Bahrick & R. Lickliter, 2000; L. E. Bahrick, R. Lickliter, & R. Flom, 2004) detection of and memory for nonredundantly specified properties, including the visual orientation of an event, are facilitated in unimodal stimulation and attenuated in bimodal stimulation in early development. Later in development, however, nonredundantly specified properties can be perceived and remembered in both multimodal and unimodal stimulation. The current study extended tests of these predictions to the domain of memory in infants of 3, 5, and 9 months of age. Consistent with predictions of the intersensory redundancy hypothesis, in unimodal stimulation, memory for visual orientation emerged by 5 months and remained stable across age, whereas in bimodal stimulation, memory did not emerge until 9 months of age. Memory for orientation was evident even after a 1-month delay and was expressed as a shifting preference, from novelty to null to familiarity, across increasing retention time, consistent with Bahrick and colleagues' four-phase model of attention. Together, these findings indicate that infant memory for nonredundantly specified properties of events is a consequence of selective attention to those event properties and is facilitated in unimodal stimulation. Memory for nonredundantly specified properties thus emerges in unimodal stimulation, is later extended to bimodal stimulation, and lasts across a period of at least 1 month.

Two are better than one: comparison influences infants' visual recognition memory

Despite a large literature on infants' memory for visually presented stimuli, the processes underlying visual memory are not well understood. Two studies with 4-month-olds (N=60) examined the effects of providing opportunities for comparison of items on infants' memory for those items. Experiment 1 revealed that 4-month-olds failed to show evidence of memory for an item presented during familiarization in a standard task (i.e., when only one item was presented during familiarization). In Experiment 2, infants showed robust memory for one of two different items presented during familiarization. Thus, infants' memory for the distinctive features of individual items was enhanced when they could compare items.

Growth and Visual Information Processing in Infants in Southern Ethiopia

Speed of information processing and recognition memory can be assessed in infants using a visual information processing (VIP) paradigm. In a sample of 100 infants 6-8 months of age from Southern Ethiopia, we assessed relations between growth and VIP. The 69 infants who completed the VIP protocol had a mean weight z score of -1.12 ± 1.19 SD, and length z score of -1.05 ± 1.31. The age-appropriate novelty preference was shown by only 12 infants. When age was controlled, longest look duration during familiarization was predicted by weight (sr(2) = .16, p = .001) and length (sr(2) = .05, p =.058), and mean look duration during test phases was predicted by head circumference (sr(2) = .08, p = .018) implying that growth is associated with development of VIP. These data support the validity of VIP as a measure of infant cognitive development that is sensitive to nutritional factors and flexible enough to be adapted to individual cultures.

Assoziation zwischen der Kompetenz zur Kontingenzerkennung im Alter von drei und sechs Monaten und dem Entwicklungsstand im Alter von ein und zwei Jahren

Zusammenfassung. Berichtet wird über eine Längsschnittstudie mit vier Untersuchungszeitpunkten an 87 Kindern im Alter von 3 bis 24 Monaten. Ziel war es, die Assoziationen zwischen Kompetenzen zur nicht-sozialen Kontingenzwahrnehmung mit drei und sechs Monaten und dem späteren Entwicklungsstand mit einem bzw. zwei Jahren sowie der sprachlichen Entwicklung mit zwei Jahren zu analysieren. Die Kompetenz zur Wahrnehmung nicht-sozialer Kontingenzen wurde mittels Mobile Conjugate Reinforcement Paradigma (Mobiletest) sowie Visual Expectation Paradigma (VEP) erhoben. Der Entwicklungsstand wurde mit dem Entwicklungstest 6 Monate - 6 Jahre (ET 6-6) erhoben, die sprachliche Entwicklung mittels des Sprachtests für zweijährige Kinder (SETK-2). Es zeigte sich, dass die Ergebnisse des Mobiletests mit drei Monaten signifikante Bezüge zur Sprachentwicklung mit zwei Jahren aufwiesen. Das VEP mit sechs Monaten stand ebenfalls mit der Sprachentwicklung mit zwei Jahren, zusätzlich aber auch mit der kognitiven und sozialen Entwicklung mit einem Jahr in Verbindung. Diskutiert werden neben der Notwendigkeit zu einer altersspezifischen Differenzierung zwischen den beiden Paradigmen zur Wahrnehmung nicht-sozialer Kontingenzen auch die möglichen Verbindungslinien zwischen nicht-sozialer Kontingenzwahrnehmung und Entwicklung.

Infants' attention to patterned stimuli: developmental change from 3 to 12 months of age

To examine the development of look duration as a function of age and stimulus type, 14- to 52-week-old infants were shown static and dynamic versions of faces, Sesame Street material, and achromatic patterns for 20 s of accumulated looking. Heart rate was recorded during looking and parsed into stimulus orienting, sustained attention, and attention termination phases. Infants' peak look durations indicated that prior to 26 weeks there was a linear decrease with age for all stimuli. Older infants' look durations continued to decline for patterns but increased for Sesame Street and faces. Measures of heart rate change during sustained attention and the proportion of time spent in each phase of attention confirmed infants' greater engagement with the more complex stimuli.

What does it look like and what can it do? Category structure influences how infants categorize

Despite a large body of research demonstrating the kinds of categories to which infants respond, few studies have directly assessed how infants' categorization unfolds over time. Four experiments used a visual familiarization task to evaluate 10-month-old infants' (N = 98) learning of exemplars characterized by commonalities in appearance or function. When learning exemplars with a common function, infants initially responded to the common feature, apparently forming a category, and only learned the individual features with more extensive familiarization. When learning exemplars with a common appearance, infants initially learned the individual features and apparently only formed a category with more extensive familiarization. The results are discussed in terms of models of category learning.

Familiarization, attention, and recognition memory in infancy: an event-related potential and cortical source localization study

This study investigated the effects of familiarization and attention on event-related potential (ERP) correlates of recognition memory in infants. Infants 4.5, 6, or 7.5 months of age were either familiarized with 2 stimuli that were used during later testing or presented 2 stimuli that were not used later. Then, infants were presented with a recording of Sesame Street to elicit attention or inattention and presented with familiar and novel stimuli. A negative ERP component over the frontal and central electrodes (Nc) was larger in the preexposure familiarization group for novel- than for familiar-stimulus presentations, whereas the Nc did not differ for the group not receiving a familiarization exposure. Spatial independent components analysis of the electroencephelogram and "equivalent current dipole" analysis were used to examine putative cortical sources of the ERP components. The cortical source of Nc was located in areas of prefrontal cortex and anterior cingulate cortex.

Long-term memory for music: infants remember tempo and timbre

We show that infants' long-term memory representations for melodies are not just reduced to the structural features of relative pitches and durations, but contain surface or performance tempo- and timbre-specific information. Using a head turn preference procedure, we found that after a one week exposure to an old English folk song, infants preferred to listen to a novel folk song, indicating that they remembered the familiarized melody. However, if the tempo (25% faster or slower) or instrument timbre (harp vs. piano) of the familiarized melody was changed at test, infants showed no preference, indicating that they remembered the specific tempo and timbre of the melodies. The results are consistent with an exemplar-based model of memory in infancy rather than one in which structural features are extracted and performance features forgotten.

The development of visual short-term memory capacity in infants

Four experiments assessed visual short-term memory capacity in 4- to 13-month-old infants by comparing their looking to changing and nonchanging stimulus streams presented side by side. In each stream, 1 to 6 colored squares repeatedly appeared and disappeared. In changing streams, the color of a different randomly chosen square changed each time the display reappeared; the colors remained the same in nonchanging streams. Infants should look longer at changing streams, but only if they can remember the colors of the squares. The youngest infants preferred changing streams only when the displays contained one object, whereas older infants preferred changing streams when the displays contained up to 4 objects. Thus, visual short-term memory capacity increases significantly across the first year of life.