Melissa W. Clearfield

Amount Versus Number: Infants' Use of Area and Contour Length to Discriminate Small Sets

Previous research has reported that infants use amount rather than number to discriminate small sets (Clearfield & Mix, 1999). This study sought to replicate and extend this finding. Experiment 1 confirmed that infants respond to changes in contour length but not to changes in number when contour length is controlled. However, contour length and area were confounded in this experiment and the original study. To determine what specific measure of spatial extent infants use to discriminate small sets, Experiment 2 included 2 conditions that varied either area or contour length, but not both. As before, infants responded to the changes in spatial extent-either contour length alone or area alone-but not to the changes in number.

Learning by looking: Infants' social looking behavior across the transition from crawling to walking.

This study investigated how infants gather information about their environment through looking and how that changes with increases in motor skills. In Experiment 1, 9.5- and 14-month-olds participated in a 10-min free play session with both a stranger and ambiguous toys present. There was a significant developmental progression from passive to active social engagement, as evidenced by younger infants watching others communicate more and older infants making more bids for social interaction. Experiment 2 examined longitudinally the impact of age and walking onset on this progression. The transition to independent walking marked significant changes in how often infants watched others communicate and made active bids for social interaction. Results suggest that infants transition from passive observers as crawlers to active participants in their social environment with the onset of walking.

Cue salience and infant perseverative reaching: tests of the dynamic field theory

Skilled behavior requires a balance between previously successful behaviors and new behaviors appropriate to the present context. We describe a dynamic field model for understanding this balance in infant perseverative reaching. The model predictions are tested with regard to the interaction of two aspects of the typical perseverative reaching task: the visual cue indicating the target and the memory demand created by the delay imposed between cueing and reaching. The memory demand was manipulated by imposing either a 0- or a 3-second delay, and the salience of the cue to reach was systematically varied. Infants demonstrated fewer perseverative errors at 0-delay versus 3-second delay based on the cue salience, such that a more salient visual cue was necessary to overcome a longer delay. These results have important implications for understanding both the basic perceptual-motor processes that produce reaching in infants and skilled flexible behavior in general.

The effects of SES on infant and maternal diurnal salivary cortisol output.

The present study directly compared diurnal salivary cortisol output and maternal-infant synchrony in low and high socio-economic status (SES) mother-infant dyads. Saliva cortisol samples were collected from 32 6-12-month-old infants and their mothers on the same day in the morning, afternoon and evening, and assayed for free cortisol concentration. Low-SES infants and mothers exhibited higher average salivary cortisol output, without dysregulation, compared to high-SES infants. Low-SES infants and mothers also showed reduced synchrony in cortisol output compared to high-SES infants and mothers. Results are discussed with respect to maternal sensitivity and early stress reduction interventions.

SES affects infant cognitive flexibility

Cognitive flexibility requires processing multiple sources of information and flexible adaptation of behavioral responses. Poverty negatively impacts cognitive control in young children, but its effects on infants are not well-understood. This study investigated longitudinally the development of cognitive flexibility in low-income infants. Thirty-two infants (15 low-SES, 17 high-SES) were tested at 6, 9, and 12 months of age. Cognitive flexibility was measured with a perseverative reaching task, where infants were taught to reach to one location and then asked to switch to a second location. High-SES infants replicated the typical developmental trajectory, reaching randomly at 6 months, perseverating at 9 months, and reaching correctly at 12 months. In contrast, the low-SES infants showed a delayed pattern, reaching correctly at 6 months, randomly at 9 months, and perseverating at 12 months. Links between cognitive flexibility and frontal cortex development are explored as a potential mechanism.

Familiarization in Infants' Perception of Addition Problems.

Previous research suggests that infants can calculate simple arithmetic (Wynn, 1992). This study sought to replicate this finding and examine how familiarization may influence response. Experiment 1 confirmed that 3- to 5-month-old infants looked longer at an incorrect outcome (1 + 1 = 1) when no familiarization trials were presented. Experiment 2 presented infants with 8 familiarization trials (either to the possible or impossible mathematical event). When familiarized to the incorrect outcome, infants looked longer at the correct outcome; however, when familiarized to the correct outcome, infants showed no preference for either display. Experiment 3 confirmed that infants could have become familiarized to both 1 and 2 dolls during the familiarization to the possible event and raised the possibility that infants may not process the display as a mathematical event, but rather as a series of unconnected stimuli.

Socioeconomic status affects oral and manual exploration across the first year.

Oral and manual exploration are part of the foundation of problem solving and cognition in infancy. How these develop in an at-risk population, infants in poverty, is unknown. The current study tested exploratory behaviors longitudinally at 6, 9, and 12 months in infants from high- and low-socioeconomic (SES) families. Oral exploration consisted of passive and active mouthing and looks after active mouthing. Manual exploration consisted of frequency of fingering, rotating, and transferring the object. High-SES infants replicated the trajectory previously reported in the literature, showing a decrease in mouthing and fingering and an increase in rotating and transferring (e.g., Palmer, 1989). In contrast, low-SES infants showed no change in any of the manual exploratory behaviors over the first year, thus demonstrating reduced overall levels of exploration as well as a different developmental trajectory. Results are discussed in terms of attention, potential physiological mechanisms, and implications for later problem solving.

A novel technology for investigating the dynamics of infant perseverative reaching

We designed and tested a novel technology that enables us to capture the entire stream of behavior in perseverative reaching tasks. Beyond fitting the criteria of the conventional A-not-B task, the novel technology gives us better access to the core features of perseverative reaching, such as timing, behavior history, and reinforcement. The technology allows us to quantitatively manipulate reinforcement characteristics, to accurately program onsets, delays, and stimulus durations as well as locations and salience of the targets, and to automatically record the number of reaches to each target and compute timing. We did a validation study on this new technology, investigating the influence of a number of novel factors on perseverative reaching. We replicated the A-not-B phenomenon and associated developmental changes. In addition, results demonstrated that the new technology offers insights into infants’ behavior beyond the first reaching action. Moreover, data collection is fully automated, yielding precise, quantitative data. Future studies using this technology will capitalize on the salient advantages of this technology to more precisely measure goal-directed actions and understand the development of reaching skill.