Hillary Hadley

A Mechanistic Approach to Cross-Domain Perceptual Narrowing in the First Year of Life

Language and face processing develop in similar ways during the first year of life. Early in the first year of life, infants demonstrate broad abilities for discriminating among faces and speech. These discrimination abilities then become tuned to frequently experienced groups of people or languages. This process of perceptual development occurs between approximately 6 and 12 months of age and is largely shaped by experience. However, the mechanisms underlying perceptual development during this time, and whether they are shared across domains, remain largely unknown. Here, we highlight research findings across domains and propose a top-down/bottom-up processing approach as a guide for future research. It is hypothesized that perceptual narrowing and tuning in development is the result of a shift from primarily bottom-up processing to a combination of bottom-up and top-down influences. In addition, we propose word learning as an important top-down factor that shapes tuning in both the speech and face domains, leading to similar observed developmental trajectories across modalities. Importantly, we suggest that perceptual narrowing/tuning is the result of multiple interacting factors and not explained by the development of a single mechanism.

The lasting effects of process-specific versus stimulus-specific learning during infancy.

The capacity to tell the difference between two faces within an infrequently experienced face group (e.g. other species, other race) declines from 6 to 9 months of age unless infants learn to match these faces with individual-level names. Similarly, the use of individual-level labels can also facilitate differentiation of a group of non-face objects (strollers). This early learning leads to increased neural specialization for previously unfamiliar face or object groups. The current investigation aimed to determine whether early conceptual learning between 6 and 9 months leads to sustained behavioral advantages and neural changes in these same children at 4-6 years of age. Results suggest that relative to a control group of children with no previous training and to children with infant category-level naming experience, children with early individual-level training exhibited faster response times to human faces. Further, individual-level training with a face group - but not an object group - led to more adult-like neural responses for human faces. These results suggest that early individual-level learning results in long-lasting process-specific effects, which benefit categories that continue to be perceived and recognized at the individual level (e.g. human faces).

The developmental time course and topographic distribution of individual-level monkey face discrimination in the infant brain

ABSTRACT The ability to discriminate between faces from unfamiliar face groups has previously been found to decrease across the first year of life. Here, individual‐level discrimination of faces within a previously unfamiliar group was investigated by measuring neural responses to monkey faces. Six‐ and 9‐month‐old infants (n = 42) completed a Fast Periodic Visual Stimulation (FPVS) task while steady state visual evoked potentials (ssVEPs) were recorded. Using an oddball task design (e.g., infrequent changes in face identity) faces were presented at a 6 Hz (1 face approximately every 167 ms) stimulation rate and every 1.2 Hz different individual monkey faces were presented. Significant SNRs at 1.2 Hz in both 6‐ and 9‐month‐old infants suggest that neural responses, recorded over posterior scalp regions, remain sensitive to individual‐level differences within an unfamiliar face group despite previous behavioral evidence of decreased discrimination. However, the topographic distribution of the 1.2 Hz response varied by age, suggesting that 6‐ and 9‐month‐old infants are using different neural populations to discriminate unfamiliar faces at the individual level. HIGHLIGHTSSix‐ and 9‐month‐olds show neural evidence of discrimination of monkey faces.The topographic distribution of neural responses differed by age.Six‐ and 9‐month‐olds may use different neural systems for face discrimination.

Neural and behavioral effects of subordinate-level training of novel objects across manipulations of color and spatial frequency

Perceptual expertise is marked by subordinate‐level recognition of objects in the expert domain. In this study, participants learned one family of full‐color, artificial objects at the subordinate (species) level and another family at the basic (family) level. Discrimination of trained and untrained exemplars was tested before and after training across several image manipulations [full‐color, grayscale, low spatial frequency (LSF) and high spatial frequency (HSF)] while event‐related potentials (ERPs) were recorded. Regardless of image manipulation, discrimination (indexed by d’) of trained and of untrained exemplars was enhanced after subordinate‐level training, but not after basic‐level training. Enhanced discrimination after subordinate‐level training generalized to untrained exemplars and to grayscale images and images in which LSF or HSF information was removed. After training, the N170 and N250, recorded over occipital and occipitotemporal brain regions, were both more enhanced after subordinate‐level training than after basic‐level training. However, the topographic distribution of enhanced responses differed across components. The N170 latency predicted reaction time after both basic‐level training and subordinate‐level training, highlighting an association between behavioral and neural responses. These findings further elucidate the role of the N170 and N250 as ERP indices of subordinate‐level expert object processing and demonstrate how low‐level manipulations of color and spatial frequency impact behavior and the N170 and N250 components independent of training or expertise.

Babies get it right.

Infants use a region on the right side of their brain to distinguish between human faces and objects.