Peter S. Kaplan

Child‐Directed Speech Produced by Mothers with Symptoms of Depression Fails to Promote Associative Learning in 4‐Month‐Old Infants

Child-directed (CD) speech segments produced by 20 mothers who varied in self-reported symptoms of depression, recorded during a structured play interaction with their 2- to 6-month-old infants, were used as conditioned stimuli with face reinforcers in a conditioned attention paradigm. After pairings of speech segments and faces, speech segments were assessed for their ability to increase time spent looking at a novel checker-board pattern (summation test) using 225 4-month-old infants of nondepressed mothers. Significant positive summation, an index of associative learning, was obtained in groups of infants tested with speech produced by mothers with comparatively fewer self-reported symptoms of depression (Beck Depression Inventory or BDI < or = 15). However, significant positive summation was not achieved using speech samples produced by mothers with comparatively more symptoms of depression (BDI > 15). These results indicate that the CD speech produced by mothers with symptoms of depression does not promote associative learning in infants.

Individual differences in contrast sensitivity functions: Longitudinal study of 4-, 6- and 8-month-old human infants

Contrast sensitivity functions (CSFs) of 25 infants were measured longitudinally at 4, 6 and 8 months of age using a preferential-looking method and the method of constant stimuli. Sine-wave gratings varied from 0.27 to 4.32 c/deg, contained eight unattenuated cycles (with edges tapered to uniform gray), and rose to the desired contrast in 2 sec. (1) The average CSF was described on log-log coordinates by a band-pass function. With development it increased in overall sensitivity to contrast, shifted its peak toward slightly higher spatial frequencies, and increased its high frequency cutoff. (2) Log sensitivity at the CSF peak was slightly higher for female than male infants at 6 months, consistent with the hypothesis that vernier acuity (which also may differ between the sexes at this age) is partly mediated by analyzers tuned to low frequencies. (3) Within age groups the individual differences were such that log sensitivities for neighboring spatial frequencies generally correlated more highly than distant frequencies. With development the correlations among distant frequencies below 1.0 c/deg increased. Monte Carlo simulations of a model that shifts spatial analyzers to higher frequencies with age reproduced these results but simulations of adultlike, unshifting analyzers did not. (4) Measures taken 2 months apart tended to correlate more highly than those taken 4 months apart, though some individual differences in the CSF peak remained stable over 4 months.

Infant-directed versus adult-directed speech as signals for faces

The effectiveness of infant- and adult-directed (ID and AD) speech as signals for adult faces was studied. In the pairing phase of Experiment 1, 4-month-olds received 6 presentations of an ID or AD speech segment that either preceded (forward pairings) or followed (backward pairings) the presentation ofa smiling face. In the summation test phase, infants received 4 novel checkerboard pattern presentations, 2 with and 2 without the speech segment. Only infants in the ID forward pairing condition exhibited significant positive summation. In Experiment 2, the differences between ID and AD forward pairing groups were replicated with different speech exemplars. In Experiment 3, an ID speech segment that was paired with a smiling or sad face elicited significant positive summation, while one paired with a fearful or angry face did not. These differences in visual responding were not accompanied by differences in infant facial affect. Ways in which ID speech may facilitate associative learning are discussed.

Role of Clinical Diagnosis and Medication Use in Effects of Maternal Depression on Infant-Directed Speech

Infant-directed (ID) speech was recorded from mothers as they interacted with their 4- to 12-month-old infants. Hierarchical regression analyses revealed that two variables, age of the mother and mothers diagnosed depression, independently accounted for significant proportions of the variance in the extent of change in fundamental frequency (ΔF0). Specifically, depressed mothers produced ID speech with smaller ΔF0 than did nondepressed mothers, and older mothers produced ID speech with larger ΔF0 than did younger mothers. Mothers who were taking antidepressant medication and who were diagnosed as being in at least partial remission produced ID speech with mean ΔF0 values that were comparable to those of nondepressed mothers. These results demonstrate explicit associations between major depressive disorder and an acoustic attribute of ID speech that is highly salient to young infants.

Individual differences in contrast sensitivity functions: the first four months of life in humans

Contrast sensitivity functions of forty 4-month-old human infants were measured using a preferential-looking method and the method of constant stimuli. Circular sinewave gratings varied from 0.27 to 1.08 c/deg, contained eight unattenuated cycles (with edges tapered to uniform gray), and rose to the desired contrast in 2 sec. Log contrast sensitivities for variables close in spatial frequency correlated more highly than those that were farther apart in these data, and in data of 1-, 2-, and 3-month-olds from Banks and Salapatek [(1981) Journal of Experimental Child Psychology, 31, 1-45]. Factor analyses yielded at least two frequency-tuned factors per age group. Monte Carlo simulations of a quantitative model that shifts spatial mechanisms to higher frequencies with age reproduced the results for 4-month-olds, but simulations of adultlike, unshifting mechanisms did not. The data are consistent with the following conclusions: (a) individual differences in the sensitivity of spatial mechanisms may explain some individual differences in CSFs; (b) factor analysis may help to estimate mechanism tuning; and (c) spatial mechanisms may shift to higher frequencies during development.

Sensitization and dishabituation of infant visual fixation

Abstract Dishabituation is defined as the renewed response to a familiarized stimulus upon its retest after the introduction of a novel-stimulus. Two experiments tested an account of dishabituation of infant visual fixation based on the hypothesis that a general, state-dependent sensitization produced by the novel-stimulus energizes responding to any subsequent stimulus. However, this sensitization is thought to be time-dependent, so that increasing delays between the termination of the novel stimuli and the onset of the retest should lead to diminished dishabituation. In Experiment 1, the time between the end of familiarization and the start of the retest of the familiarized pattern was held constant and the temporal location in that inverval of 2 novel stimulus presentations was manipulated. Significant dishabituation was observed only when the novel stimuli occurred shortly before the retest. In Experiment 2, the number of novel-stimulus presentations was systematically manipulated and the magnitude of dishabituation was observed. Significant dishabituation occurred after 2 or 4, but not after 6, novel-stimulus presentations. These findings were consistent with the sensitization explanation of dishabituation, and cast doubt on an explanation of this form of dishabituation based on schema-change.

Dishabituation of visual attention in 4-month-olds by infant-directed frequency sweeps

Abstract The effects on visual attention in 4-month-olds of rising, falling, and bell-shaped frequency sweeps taken from natural, infant-directed (ID), female speech were investigated in a habituation-dishabituation paradigm. In both experiments, a checkerboard pattern was presented for 10 s on each of 12 trials, with a 10-s series of five brief sweeps occuring simultaneously with the visual stimulus on the ninth trial. In Experiment 1, infants exhibited renewed visual attention when rising and bell-shaped, but not falling, frequency sweeps were presented. Renewed attention also occured on the subsequent (10th) trial in which the check pattern was again presented alone. However, this Thompson-Spencer dishabituation effect occured only following the rising sweep. In Experiment 2, visual attention increased significantly during presentations of both the rising and falling sweeps, and Thompson-Spencer dishabituation was again observed only following the rising sweep. Synthetic sweep stimuli modeled on the fundamental frequency (F 0 ) of the rising sweep similarly increased gaze duration but produced no Thompson-Spencer dishabituation. Results are discussed in terms of the attention-controlling and arousing properties of ID frequency-modulated sweeps.

Depression Diagnoses and Fundamental Frequency-Based Acoustic Cues in Maternal Infant-Directed Speech

F0-based acoustic measures were extracted from a brief, sentence-final target word spoken during structured play interactions between mothers and their 3- to 14-month-old infants and were analyzed based on demographic variables and DSM-IV Axis-I clinical diagnoses and their common modifiers. F0 range (ΔF0) was negatively correlated with infant age and number of children. ΔF0 was significantly smaller in clinically depressed mothers and mothers diagnosed with depression in partial remission, relative to nondepressed mothers, mothers diagnosed with depression in full remission, and those diagnosed with depressive disorder not otherwise specified. ΔF0 was significantly lower in mothers experiencing their first major depressive episode relative to mothers with recurrent depression. Deficits in ΔF0 were specific to diagnosed clinical depression, and were not well predicted by elevated self-report scores only or by diagnosed anxiety disorders. Mothers with higher ΔF0 had infants with reportedly larger productive vocabularies, but depression was unrelated to vocabulary development. Implications for cognitive-linguistic development are discussed.

A developmental decline in the learning-promoting effects of infant-directed speech for infants of mothers with chronically elevated symptoms of depression.

Infants of mothers who varied in symptoms of depression were tested at 4 and 12 months of age for their ability to associate a segment of an unfamiliar non-depressed mothers infant-directed speech (IDS) with a face. At 4 months, all infants learned the voice-face association. At 12 months, despite the fact that none of the mothers were still clinically depressed, infants of mothers with chronically elevated self-reported depressive symptoms, and infants of mothers with elevated self-reported depressive symptoms at 4 months but not 12 months, on average did not learn the association. For infants of mothers diagnosed with depression in remission, learning at 12 months was negatively correlated with the postpartum duration of the mothers depressive episode. At neither age did extent of pitch modulation in the IDS segments correlate with infant learning. However, learning scores at 12 months correlated significantly with concurrent maternal reports of infant receptive language development. The roles of the duration and timing of maternal depressive symptoms are discussed.

Sensitizing properties of spectral lights in 4-month-old human infants

Previous studies of infant attention, learning, and memory have revealed that certain stimulus properties may increase an infants arousal or excitation level, thereby increasing responsiveness and facilitating the encoding and processing of information. In a series of experiments aimed at identifying stimulus determinants of sensitization, we examined visual responses from 4-month-old infants to spectral lights. Habituation data were obtained from 92 full-term infants separated into one of five groups. Each group viewed either a broadband white light (correlated color temperature approximately 2800 K) or one of four different spectral lights (lambda d = 470, 510, 570, or 650 nm) approximately corresponding to the elemental hues blue, green, yellow and red, respectively, for adults with normal trichromatic vision. Stimuli were equated in luminous efficiency for a standard infant observer. Stimulus fixation was recorded for twelve 10-s presentations, each separated by 10-s interstimulus intervals (ISIs). The results show that mean fixation times to the red and green lights were significantly greater than those for the blue and white light. Mean fixation time for the yellow light was also reduced (significantly) compared to the red but not the green light. These results suggest that the chromatic properties of red and green spectral lights may be more sensitizing to infants than those of the blue, yellow, or white lights.