Search

This study examined if two-year-olds with ASD can update mental representations on the basis of verbal input. In an eye-tracking study, toddlers with ASD and typically-developing nonverbal age-matched controls were exposed to visual or verbal information about a change in a recently encoded scene, followed by an outcome that was either congruent or incongruent with that information. Findings revealed that both groups looked longer at incongruent outcomes, regardless of information modality, and despite the fact that toddlers with ASD had significantly lower measured verbal abilities than TD toddlers. This demonstrates that, although there is heterogeneity on the individual level, young toddlers with ASD can succeed in updating their mental representations on the basis of verbal input in a low-demand task.

The dominant view of children's memory is that it is slow to develop and is inferior to adults'. Here we pitted 4-year-old children against adults in a test of verbatim recall of verbal material. Parents read a novel rhyming verse (and an integrated word list) as their child's bedtime story on ten consecutive days. A group of young adults listened to the verse, matching the exposure of children. All participants subsequently performed a free-recall of the verse, verbatim. (Parents and young adults knew they would be tested; children did not.) Four-year-olds significantly outperformed both their parents and the young adults. There were no significant differences in the ability to recall the gist of the verse, nor the integrated word list, allaying concerns about differences in engagement or motivation. Verbatim recall of verse is a skill amenable to practice, and children, we argue, by virtue of the prominence of verse in their culture and their reliance on oral transmission, have honed this skill to exceed adults'.

We tested 8- and 10-month-old infants' visual working memory (VWM) for object-location bindings--"what is where"--with a novel paradigm, Delayed Match Retrieval, that measured infants' anticipatory gaze responses (using a Tobii T120 eye tracker). In an inversion of Delayed-Match-to-Sample tasks and with inspiration from the game "Memory," in test trials, three face-down virtual "cards" were presented. Two flipped over sequentially (revealing, e.g. a swirl pattern and then a star), and then flipped back face-down. Next, the third card was flipped to reveal a match (e.g. a star) to one of the previously seen, now face-down cards. If infants looked to the location where the (now face-down) matching card had been shown, this was coded as a correct response. To encourage anticipatory looks, infants subsequently received a reward (a brief, engaging animation) presented at that location. Ten-month-old infants performed significantly above chance, showing that their VWM could hold object-location information for the two cards. Overall, 8-month-olds' performance was at chance, but they showed a robust learning trend. These results corroborate previous findings (Kaldy & Leslie, 2005; Oakes, Ross-Sheehy & Luck, 2006) and point to rapid development of VWM for object-location bindings. However, compared to previous paradigms that measure passive gaze responses to novelty, this paradigm presents a more challenging, ecologically relevant test of VWM, as it measures the ability to make online predictions and actively localize objects based on VWM. In addition, this paradigm can be readily scaled up to test toddlers or older children without significant modification.

A number of studies have demonstrated that individuals with autism spectrum disorders (ASDs) are faster or more successful than typically developing control participants at various visual-attentional tasks (for reviews, see Dakin and Frith in "Neuron" 48:497-507, 2005; Simmons et al. in "Vis Res" 49:2705-2739, 2009). This "ASD advantage" was first identified in the domain of visual search by Plaisted et al. ("J Child Psychol Psychiatry" 39:777-783, 1998). Here we survey the findings of visual search studies from the past 15 years that contrasted the performance of individuals with and without ASD. Although there are some minor caveats, the overall consensus is that--across development and a broad range of symptom severity--individuals with ASD reliably outperform controls on visual search. The etiology of the ASD advantage has not been formally specified, but has been commonly attributed to 'enhanced perceptual discrimination', a superior ability to visually discriminate between targets and distractors in such tasks (e.g. O'Riordan in "Cognition" 77:81-96, 2000). As well, there is considerable evidence for impairments of the attentional network in ASD (for a review, see Keehn et al. in "J Child Psychol Psychiatry" 37:164-183, 2013). We discuss some recent results from our laboratory that support an attentional, rather than perceptual explanation for the ASD advantage in visual search. We speculate that this new conceptualization may offer a better understanding of some of the behavioral symptoms associated with ASD, such as over-focusing and restricted interests.

In this study, 6-month-old infants' visual working memory for a static feature (color) and a dynamic feature (rotational motion) was compared. Comparing infants' use of different features can only be done properly if experimental manipulations to those features are equally salient (Kaldy & Blaser, 2009; Kaldy, Blaser, & Leslie, 2006). The interdimensional salience mapping method was used to find two objects that each were one Just Salient Difference from a common baseline object (N = 16). These calibrated stimuli were then used in a subsequent two-alternative forced-choice preferential looking memory test (N = 28). Results showed that infants noted the color change, but not the equally salient change in rotation speed.

Plaisted, O'Riordan and colleagues (Plaisted, O'Riordan & Baron-Cohen, 1998; O'Riordan, 2004) showed that school-age children and adults with Autism Spectrum Disorder (ASD) are faster at finding targets in certain types of visual search tasks than typical controls. Currently though, there is very little known about the visual search skills of very young children (1-3-year-olds)--either typically developing or with ASD. We used an eye-tracker to measure looking behavior, providing fine-grained measures of visual search in 2.5-year-old toddlers with and without ASD (this representing the age by which many children may first receive a diagnosis of ASD). Importantly, our paradigm required no verbal instructions or feedback, making the task appropriate for toddlers who are pre- or nonverbal. We found that toddlers with ASD were more successful at finding the target than typically developing, age-matched controls. Further, our paradigm allowed us to estimate the number of items scrutinized per trial, revealing that for large set size conjunctive search, toddlers with ASD scrutinized as many as twice the number of items as typically developing toddlers, in the same amount of time.

What kind of featural information do infants rely on when they are trying to recognize a previously seen object? The question of whether infants use certain features (e.g., shape or color) more than others (e.g., luminance) can only be studied legitimately if visual salience is controlled, as the magnitude of feature values--how noticeable and interesting they are--will affect results. We employed a novel methodology, interdimensional salience mapping, that allowed us to quantify and calibrate salience changes along shape, luminance, and color feature dimensions. We then compared 9-month-old infants' identification of objects, employing feature changes that were equally salient. These results show that infants more readily identify objects on the basis of color and shape than luminance. Additionally, we show that relative salience changes rapidly in infancy--in particular, we found significantly higher salience thresholds for color in younger (6.5-month-old) infants--but that individual differences within an age group are remarkably modest. (Contains 6 figures and 7 footnotes.)

We report a new method for calibrating differences in perceptual salience across feature dimensions, in infants. The problem of inter-dimensional salience arises in many areas of infant studies, but a general method for addressing the problem has not previously been described. Our method is based on a preferential looking paradigm, adapted to determine the relative salience of two stimuli. We report here on the case of stimuli differing in color and luminance, though the method has wider potential. We were able to determine on a psychophysical curve the point at which a color contrast was equally salient to infants as a given luminance contrast. We then used these calibrated, "iso-salient" stimuli in an object memory study. Results showed that 6.5-month-old infants noticed a color, but not a luminance, change while tracking an occluded object. Our method should have numerous applications in the study of bottom-up effects on infant attention and visual working memory.

Infants' abilities to identify objects based on their perceptual features develop gradually during the first year and possibly beyond. Earlier we reported [Kaldy, Z., & Leslie, A. M. (2003). Identification of objects in 9-month-old infants: Integrating "what" and "where" information. Developmental Science, 6, 360-373] that infants at 9 months of age are able to use shape information to identify two objects and follow their spatiotemporal trajectories behind occlusion. On the other hand, another recent study suggests that infants at 4-5 months of age cannot identify objects by features and bind them to locations [Mareschal, D., & Johnson, M. H. (2003). The ''what'' and ''where'' of object representations in infancy. Cognition, 88, 259-276]. In the current study, we investigated the developmental steps between these two benchmark ages by testing 6.5-month-old infants. Experiment 1 and 2 adapted the paradigm used in our previous studies with 9-month-olds that involves two objects hidden sequentially behind separate occluders. This technique allows us to address object identification and to examine whether only one or both object identities are being tracked. Results of experiment 1 showed that 6.5-month-old infants could identify at least one of two objects based on shape and experiment 2 found that this ability holds for only one, the last object hidden. We propose that at this age, infants' working memory capacity is limited to one occluded object if there is a second intervening hiding. If their attention is distracted by an intervening object during the memory maintenance period, the memory of the first object identity appears to be lost. Results of experiment 3 supported this hypothesis with a simpler one-screen setup. Finally, results of experiment 4 show that temporal decay of the memory trace (without an intervening hiding) by itself cannot explain the observed pattern of results. Taken together, our findings suggest that at six months of age infants can store but a single object representation with bound shape information, most likely in the ventral stream. The memory span of one may be due to immaturity of the neural structures underlying working memory such that intervening items overwrite the existing storage.

Discusses Needham's findings that infants individuate objects by feature, within the framework of brain mechanisms that index or track individual objects, drawing upon theories of attention and working memory developed in the study of adults. Considers Needham's work as contributing to an understanding of categorization and the effect of object history on individuation of objects in a complex display. (JPB)