Reading and cognitive abilities: Longitundinal studies of brain and behavior changes in young children

Annals of Dyslexia, 2002 by Molfese, Dennis L, Molfese, Victoria J, Key, Sasha, Modglin, Arlene, Et al

This paper focuses on methods useful for identifying differences in the development of language reading abilities in children that rely on measures of brain responses and behavioral assessments. Findings from longitudinal and cross-sectional studies using brain and behavior measures are described, along with findings from research designed to influence changes in brain and behavioral responses through training. The findings show differences in event-related potentials (ERP) responses recorded at birth that are related to a child's later performance on language and reading tasks. Such findings point to a strong biological influence on the development of language and reading skills. However, other findings show that the influence of biological factors on brain processing can be modified through learning. In fact, several studies show that even brief periods of stimulation and opportunities for learning can produce changes in the brain's ERP repsonses. Such findings suggest that new approaches to evaluating the effectiveness of interventions might change the rate and likelihood of developmental changes.

The role of phonological processing in the development of language and reading abilities has received much research attention. Phonological processing refers to the ability to discriminate1 phonetic contrasts, and includes discrimination of speech sounds and categorical perception (voice-onset-time, place of articulation) as well as the ability to segment and manipulate phonemes and larger units. Some phonological skills important for analyzing the sound patterns in spoken words are present at or near birth and others develop in early infancy. Young infants discriminate between speech sounds that contain phonetic contrasts characteristic of their language environments, and young infants also appear to be sensitive to phonetic contrasts characteristic of other languages (Eilers, 1977; Eilers, Wilson, & Moore, 1977; Eimas, Siqueland, Jusczyk, & Vigorito, 1971; D. Molfese & V Molfese, 1979a, 1979b, 1980, 1985). This sensitivity changes in later infancy toward an increasing sensitivity to contrasts unique to the infant's language environment, a change that appears to facilitate language acquisition. With further development, preschool children are able to segment spoken monosyllable words into onsets and rimes, and thus to play nursery rhyme games (Vellutino & Scanlon, 1987). As they continue to develop, children learn to segment polysyllabic words into syllables as they approach kindergarten age and monosyllabic words into phonemes around first grade (Liberman, Cooper, Shankweiler, & Studdert-Kennedy, 1967). Over the past decade a consensus of findings has emerged among researchers that phonological processing skills are fundamental to language development and to subsequent reading abilities (Brady, 1991; Fletcher, Foorman, Shaywitz, & Shaywitz, 1999; Wagner, Torgesen, & Rashotte, 1994).

Many of these studies of phonological processing have combined different methodologies in an effort to broadly evaluate the variety of factors that influence the development of language and reading abilities. This paper focuses on methods useful for identifying differences in the development of language and reading abilities in children that rely on measures of brain responses and behavioral assessments. Findings from these methods are described, along with findings from research designed to influence changes in brain and behavioral responses through training. Together, these findings show that even behaviors that appear to be strongly influenced by biological mechanisms can be influenced through training activities.

BRAIN RESPONSES

Brain-behavior relations have been a long-standing interest of researchers and theorists. This interest led to the development of methodologies for measuring brain responses, a useful and relatively new approach to studying developmental issues. Techniques such as electroencephalography (EEG), eventrelated potentials (ERPs), and brainstem evoked response (BSER) all share a common approach to cortical electrophysiology (scalp electrodes are used to detect electrical activity generated by neurons in the brain). A portion of this electrical signal passes through the brain and skull where it can be measured on the scalp. By positioning recording electrodes on the scalp's surface, the minute electrical discharges (approximately 5 to 10 (mu)V, or millionths of a volt) can be detected, amplified, and analyzed. The end result is a read-out of the ongoing electrical discharges (in the form of continuous brainwaves) produced during activity (e.g., sleeping, listening to music, reading) across time.

The brain measure of interest in this paper is the eventrelated potential (ERP), a portion of ongoing EEG that is timelocked to the onset of a specific stimulus (see Figure 1). ERPs are characterized by a complex waveform that varies in amplitude and frequency, and its distribution across the scalp over time. ERPs are thought to reflect ongoing brain processing triggered by stimulus events. Fluctuations in the amplitude (height of the wave) or latency (delay from stimulus onset) of various positive and negative peaks within the ERP waveform occur at different points throughout its time course (Callaway, Tueting, & Koslow, 1978; Rockstroh, Elbert, Birbaumer, & Lutzenberger, 1982). It is these fluctuations in peaks at different time points and at different scalp recording sites (e.g., frontal, parietal, temporal) that serve as data in research studies. Research over the past 70 years demonstrated that the time-locked ERP can be used to effectively study both general and specific aspects of responses to eliciting events in the external as well as internal environment (D. Molfese, 1978a, 1978b). The ERP also is used to study an individual's perceptions and decisions during tasks or following a learning situation (D. Molfese, 1983; D. Molfese & D. Molfese, 1996; Nelson & Salapatek, 1986; Ruchkin, Sutton, Munson, & Macar, 1981). Since the ERP technique does not require a planned and overt response from individuals from whom it is recorded, ERP techniques are particularly well suited for the neuropsychological study of the infant's and the child's early language development (D. Molfese, Freeman, & Palermo, 1975). One major advantage of the ERP is that it can provide very fine temporal information (one ms or less) regarding the brain's response to an eliciting input such as a speech sound. In addition, it has some spatial resolution capabilities that provide a basis for speculations concerning the distribution of brain areas generating the ERPs that subserve functions such as language, reading, and other cognitive abilities.