Biomedical subjects

G E Edmonds

Publications and source records attributed to G E Edmonds.

4 recordsLinked to original sources

PubMed2001

Eyes first! Eye processing develops before face processing in children.

Faces and eyes are critical social stimuli which adults process with ease, but how this expertise develops is not yet understood. Neural changes associated with face and eye processing were investigated developmentally using ERPs (N170), in 128 subjects (4-15 year olds and adults). Stimuli included upright faces to assess configural processing, eyes and inverted faces to assess feature-based processing. N170 was present in the youngest children with similar patterns of face sensitivity seen in adults. Development of N170 to upright faces continued until adulthood, suggesting slow maturation of configural processing. In contrast, N170 was shorter latency and much larger to eyes than faces in children and was mature by 11 years, suggesting the early presence of an eye detector, with a rapid maturational course.

Adolescent↗

PubMed2001

Direction of gaze effects on early face processing: eyes-only versus full faces.

The N170 event-related potential (ERP) reflects an early stage of face processing. We wished to determine if it would also index the intuitively important information provided by direction of gaze. Two studies were run. In one, stimuli included full faces with the eyes looking forward, to the left or closed; in the other study the stimuli included eyes-only, looking forward, left or closed. Gaze direction had no effects on amplitude, but longer latencies were found for faces with eyes closed. With eyes-only stimuli, more marked effects on latencies and borderline effects on amplitudes were seen. We suggest that there can only be limited evidence of gaze-specific sensitivity in ERP studies in humans, without eye movement.

Adult↗

PubMed2000

Is the face-sensitive N170 the only ERP not affected by selective attention?

We assessed the effect of directed attention on early neurophysiological indices of face processing, measuring the N170 event-related potential (ERP). Twelve subjects were tested on two tasks each in which they attended either to eyes only or to faces with eyes closed, presented within series of facial and control stimuli. Consistent with the ERP literature, N170 was recorded to facial stimuli at posterior temporal electrodes and a concomitant positive peak at the vertex, with latencies around 150 ms for faces and 174 ms for eyes. However, unlike fMRI studies, neither the latency nor the amplitude of the peaks were sensitive to the target/non-target status of either the eyes or the face stimuli. This suggests that early stages of face processing indexed by N 170 are automatic and unmodified by selective attention.

Adult↗

PubMed1998

Mismatch negativity to speech stimuli in 8-month-old infants and adults.

The mismatch negativity (MMN) was measured in 15 normal awake 8-month-old infants and 10 adults to the speech consonants /da/ and /ta/. ERPs were analyzed at 11 electrodes (Fz, Cz, Pz, C3, C4, T3, T4, T5, T6, P3, P4). Four-hundred trials were presented: the /da/ standards with 80% probability and the /ta/ deviants with 20% probability. The ISI was 600 ms. An MMN was observed for both adults and infants but with different scalp distributions. A clear infant MMN was observed only at C3 and T3 electrodes, whereas the adult MMN was present at Fz, Cz, C3, C4 and Pz. A repeated-measures ANOVA on the normalized summed area between 200 and 250 ms revealed an age (adult vs. infant) x electrode interaction. Paired t-tests indicated that adults and infants showed significant differences at the C3, Cz, T3, Pz and T6 electrodes. The adult MMN was largest at Cz and C3 whereas the infant MMN was largest at T3. These data are discussed in terms of possible maturational changes in the MMN.

Adult↗