Developmental trends in right hemispheric participation in reading.

Behavioral laterality tasks assessed the differential processing efficiencies of the cerebral hemispheres in younger and older reading-age children. Lateralized lexical decision task findings supported a "direct access" model of hemispheric processing for the younger children whereas the older children demonstrated a "callosal relay" pattern. A dual-task with oral and silent reading indicated that the right hand was significantly more disrupted than the left during unimanual finger tapping. The findings suggest that although the left hemisphere's involvement during reading is developmentally stable, the involvement of the right hemisphere appears to change dynamically as reading experience increases.

Hemispheric specialization for reading.

Behavioral laterality tasks with linguistic stimuli were used to assess the differential processing efficiencies of the cerebral hemispheres in right- and left-handed adults. Findings from a lateralized lexical decision task with concrete nouns supported Zaidel's (1983) "direct access" model of hemispheric functioning. A dual task consisting of oral and silent reading indicated that the right hand was significantly more disrupted than the left during unimanual finger tapping; however, some bilateral interference was observed. Taken together the findings suggest that although the left hemisphere was relatively more efficient, the right hemisphere was dynamically involved in the reading process.

Attention and attentional shift efficiency in individuals with and without mental retardation.

Adults with and without mental retardation and equal-MA children were presented with a modified Stroop paradigm to assess both attention and attentional shift efficiency. The lateralized presentation of Stroop color words, neutral words, and the subject's usual first name (Stroop/name trials) revealed that although the adults with mental retardation and the equal-MA subjects were comparable in terms of correct response latencies for the Stroop and the name trials, the former were significantly less accurate relative to the equal-MA subjects and adults without mental retardation. The random placement of low frequency name trials among the Stroop trials permitted the assessment of the subject's ability to shift attention. The lack of a greater left hemisphere interference across groups for the Stroop/name trials was not consistent with the left hemisphere advantage obtained for the reading trials. This finding was discussed in relation to the right hemisphere's involvement in tasks requiring attention.

Self-enhancing effect of social feedback on cognitive task performance.

The influence of feedback on the cognitive task performance of individuals with high and low self-esteem was assessed (Coopersmith Self-Esteem Inventory, Form A). A median split technique segregated each group (30 adults with mental retardation and 30 MA-matched controls) into high and low self-esteem individuals. All subjects performed two memory tasks (easy, difficult) but were randomly assigned to only one of three feedback conditions (social, computer, and no feedback). Findings indicated that social feedback can alter the normally positive relation between self-esteem and cognitive task performance.

Haptic asymmetries in persons with and without mental retardation.

Adults with mild mental retardation and equal-MA children and adults without mental retardation were required to (a) tactually examine single letters, two-letter words, bigrams, and Chinese characters with their right or left index finger and (b) indicate whether a visually presented stimulus was the tactually examined stimulus by saying "same" or "different." The left hand was significantly better for "same" responses and the right hand, for "different" responses, suggesting that hemispheric processing is dependent on information-processing requirements rather than type of stimulus. A left hand advantage for "same" Chinese characters by the children and adults without mental retardation was due to an increase in right hand latencies rather than a decrease in left hand latencies, again suggesting that different types of analyses are employed by the two cerebral hemispheres. Adults with mental retardation had the poorest accuracy and slowest latencies for correct "different" responses and significantly less differentiation of "same" and "different" responses (A') for all stimulus types. They identified "same" letters, words, and bigrams significantly faster than Chinese characters with their left hand and showed a trend toward the differential processing of bigrams ("same" latencies) as a function of hand.

The tachistoscopic recognition of letters under whole and partial report procedures as related to intelligence.

Investigations of the short-term memory task performance of retarded individuals have indicated that these individuals demonstrate a deficit in the mechanisms necessary for the acquisition, storage and/or retrieval of information. The present study examined the tachistoscopic letter recognition task performance of retarded and non-retarded individuals under a partial report and a whole report procedure. The results revealed that the retarded subjects did significantly more poorly relative to the non-retarded subjects under both procedures. The data were interpreted as indicating that the retarded subjects were inefficient in their strategy to make the simultaneous imput task manageable. Further, the data provided no support for the suggestion that a visual-to-auditory encoding process exists between iconic and short-term memory.

Dichotic stimulation and mental retardation.

Beginning with an overview of the complexities and current thinking with respect to the non-invasive behavioural technique of dichotic stimulation as it relates to hemispheric lateralization, the present paper examines the findings for dichotic stimulation in the area of mental retardation. A survey of the extant literature reveals that the application of dichotic stimulation with the mentally retarded has been relatively rare. However, given the paucity of studies, three conclusions can be drawn. First, when retarded subjects (excluding Down syndrome individuals) are compared to nonretarded subjects matched for mental age (MA), the ear asymmetries are invariably in the expected direction for the type of stimulus employed, however, the magnitude is variable. Second, under dichotic monitoring mentally retarded subjects (inclusive of Down syndrome individuals) demonstrate the same pattern of intrusion errors from the unattended right ear as do non-mentally retarded subjects matched for MA. Third, a majority of the dichotic stimulation studies have focused upon the "atypical" speech lateralization of Down syndrome individuals. The dichotic listening data are equivocal regarding the lateralization of speech in these individuals. However, there are two data sets that argue against their right hemispheric lateralization for speech. The first examines the intrusion errors demonstrated by Down syndrome individuals on dichotic monitoring tasks and the second examines the performance of Down syndrome subjects employing the dual-task interference paradigm.

Hemispheric processing deficits in patients with paranoid schizophrenia.

The purpose of the present study was to investigate hemispheric deficits in individuals with paranoid schizophrenia on four kinds of tasks: dichoptic viewing tasks involving verbal and nonverbal visual stimuli, and dichotic listening tasks involving verbal and nonverbal auditory stimuli. As dependent measures, both accuracy and speed of (correct) responding were measured. The sample recruited for this study consisted of 18 patients with paranoid schizophrenia, 15 outpatients with anxiety disorders, and 20 controls with no history of psychiatric disorders. Results indicated that, relative to the controls, the paranoid schizophrenic patients were less accurate and less efficient on auditory-verbal tasks requiring right hemisphere processing. Unlike the controls the paranoid schizophrenic patients manifested a lateralized left hemisphere advantage.

Retinal locus and the identification of tachistoscopically presented letters by retarded and nonretarded individuals.

Two-letter stimulus displays, differing in the magnitude of the horizontal spatial separation between the letters, were presented tachistoscopically to retarded and nonretarded persons. Assuming that the spatial separations are linearly related to retinal location, I derived an estimate of the stimulus-recognition threshold for each group by employing the method of constant stimuli. The data indicated a similar stimulus-recognition threshold and a similar decrement in the accuracy of responding as the stimulus separations increased. These findings suggested that reported differences in iconic memory between retarded and nonretarded individuals are most likely related to a postretinal stage of cognitive processing. Studies of iconic memory must take into account not only the influence of retinal locus but also the finding that, as the task becomes more difficult, retarded individuals may be less willing to respond.

Selective attention of mildly mentally retarded and nonretarded individuals.

Mildly retarded, equal-MA, and equal-CA individuals viewed tachistoscopic presentations of single-element displays under a backward visual masking paradigm. Stimulus onset asynchrony and stimulus familiarity were varied to examine the process of selective attention within the context of a proposed model of attention and memory. The data revealed that, under minimal load conditions, the internal cue-selection component of selective attention for mildly retarded subjects is comparable to that of the nonretarded subjects when familiar stimuli are employed. Alternately, when unfamiliar stimuli are employed, the equal-MA and the retarded subjects are significantly less efficient relative to the equal-CA subjects. This inefficiency is attributed to the failure of the low-MA groups to apply a durable code to the products of the orienting component of selective attention.

High-speed memory-scanning task performance of mildly mentally retarded and nonretarded individuals.

Mildly mentally retarded and CA-matched nonretarded subjects were required to memorize lists of English letters and Chinese characters varying in length from one to four elements. Single probe letters or characters were presented following memorization. The subject responded yes if the probe was a member of the memorized list or no if it was not. Subjects were encouraged to respond quickly but without making errors. Choice reaction times (RTs) were measured from probe onset to the depression of the yes or no response key upon which the index finger of the appropriate hand rested. Retarded subjects demonstrated slower overall choice mean RTs relative to the nonretarded group. Results also suggest that the processing difference lies in the memory scanning as opposed to the encoding/decision/response component of the linear model (Sternberg, 1969); however, this suggestion is limited by the disparity of the group data sets.

Iconic store readout of mildly mentally retarded and nonretarded individuals.

Mildly retarded and nonretarded subjects matched for MA and CA were required to report tachistoscopically presented linear arrays of letters differing with respect to the number of letters per array. On some trials a visual mask appeared coincidentally with or at variable intervals following the onset of the letter array. By varying information load and stimulus onset synchrony and by including a no-mask condition, it was possible to assess the iconic store readout for each of the three groups. Results revealed that the mask was influential in disrupting the sensory store readout for all groups and that the low-MA subjects demonstrated a slower sensory store readout relative to the equal-CA group. The retarded subjects demonstrated the slowest sensory store readout.

Automatic processing in mildly retarded and nonretarded persons.

Mildly retarded adults, equal mental age nonretarded children, high mental age nonretarded children, equal chronological age nonretarded adults and young nonretarded adults were required to perform a priming task (letters/digits) in which some primes were masked (visual noise mask) at just below detection levels to assess automatic processing. The critical (just below detection level) prime-mask stimulus onset asynchronies (SOAs) were established individually for each subject using the method of limits and reassessed after the experimental trials. The mean critical SOA for each of the five groups was comparable and the critical SOAs remained stable across the 120 experimental trials for all groups. The nonretarded adult subjects demonstrated semantic, categorical and orthographic priming. The mildly retarded, the equal-MA and the high-MA groups failed to demonstrate priming, and in fact, demonstrated superior performance for prime-target conditions which should have been poorest. This finding was discussed in terms of the level of specificity engendered in the priming task. Under the mask procedure, the nonretarded adult groups demonstrated semantic (letter) priming and orthographic priming, suggesting that letters (not digits) function as an analog to words which were employed in earlier masked prime lexical decision tasks. The mentally retarded, the equal-MA and the high-MA groups again failed to demonstrate priming under the mask procedure.

Iconic-memory processing of unfamiliar stimuli by retarded and nonretarded individuals.

The iconic-memory processing of unfamiliar stimuli was undertaken employing a visually cued partial-report procedure and a visual masking procedure. Subjects viewed stimulus arrays consisting of six Chinese characters arranged in a circular pattern for 100 msec. At variable stimulus-onset asynchronies, a teardrop indicator or an annulus was presented for 100 msec. Immediately upon cue offset, the subject was required to recognize the cued stimulus from a card containing a single character. Retarded subjects' performance was comparable to that of MA- and CA-matched subjects. We suggested that earlier reported iconic-memory differences between retarded and nonretarded individuals may be attributable to processes other than iconic memory.

Dichotic-listening task performance of mildly mentally retarded and nonretarded individuals.

An investigation of hemispheric lateralization of mildly mentally retarded individuals was undertaken employing the dichotic-listening paradigm. Exclusively right-handed, right-eyed, and right-footed equal-CA, equal-MA, and mildly retarded subjects were required to recognize and reject dichotic presentation-probe stimulus combinations of words and tones correctly. The dichotic presentation-probe stimulus technique was employed to minimize the influence of memory and to equate methodologically for the handling of the verbal (spoken digits) and nonverbal (complex tones) stimuli. The findings revealed a pattern of dichotic performance that was similar for the three subject groups. A right-ear advantage was obtained for the verbal stimuli; and a left-ear advantage, for the nonverbal stimuli. Performance accuracy, however, was significantly poorer for the mildly retarded subjects relative to the nonretarded subjects. Structural vs. control process differences in the information-processing system were discussed.

Mentally retarded and nonretarded individuals' attention allocation and capacity.

Eighteen mentally retarded individuals, 20 nonretarded children, and 20 nonretarded adults were exposed to three conditions of an auditory detection task. In the location condition single random nonsimultaneous English letters were presented to both ears. Subjects reported the letters to one preassigned ear. In the meaning condition rapidly presented backward letters containing infrequent target (forward) letters were presented to one ear. Subjects reported the target letters. In the both condition rapidly presented backward letters containing infrequent target (forward) letters were nonsimultaneously presented to both ears. Subjects reported the target letters to one preassigned ear. The retarded subjects and nonretarded children reported significantly fewer target letters across the location, meaning, and both conditions. These groups also demonstrated slower reaction times (RTs) relative to the adult group; however, their RTs remained constant across conditions. We concluded that developmentally immature populations are less efficient at attentional allocation and have a more limited attentional capacity.

Iconic memory deficit of mildly mentally retarded individuals.

Ten mildly mentally retarded, 10 equal-CA matched, and 10 equal-MA matched nonretarded subjects were required to recognize both verbal (two-letter words) and nonverbal (polygons) stimuli presented tachistoscopically. A backward visual masking paradigm utilizing both monoptic and dichoptic masking and varying stimulus onset asynchrony (SOA) was employed. The mildly retarded subjects were significantly poorer at the most advantageous (longest) SOAs. The monoptic mask was more effective than was the dichoptic mask, with the three groups demonstrating similar masking functions.

Semantic encoding by mildly retarded and non-retarded individuals.

Three comparable groups of mildly retarded individuals were required to encode words according to one of the levels of processing paradigm, a distinctiveness of encoding paradigm or a control condition in which encoding was not influenced in any manner. Their performance on an immediate but unexpected recognition task was compared to that of three comparable groups of equal-MA and three comparable groups of equal-CA individuals. The equal-CA group was the only group advantaged by both the levels of processing (LOP) and the distinctiveness of encoding (DOE) manipulations. The solid performance of the equal-MA subjects in the control, the LOP and the DOE conditions was attributed to the efficient use of episodic memory. The poor performance of the mildly retarded subjects across these conditions was attributed to the lack of semantic organization in permanent memory and to an inefficiency in the use of episodic memory.

Influence of visual cueing on conditioned response inhibition in retarded individuals.

A consistent finding with respect to retarded individuals is that they exhibit prolonged responding during the extinction phase of a classical eyelid-conditioning procedure relative to nonretarded individuals. The present investigation was carried out to determine whether the failure of retarded individuals to cease conditioned responding is due to a motor inhibitory deficit or to the inability to form a cognitive inhibitory set. The results indicated that, with prompting, the retarded subjects were able to inhibit the conditioned response, thereby eliminating the motor inhibitory deficit explanation for the continued conditioned responding. The data further suggested that the failure to form a cognitive inhibitory set may be related to the inability of retarded individuals to produce effective mediators.

Age-related deficits in cognitive functioning are not mediated by time of day.

Few studies have examined whether cognitive performance of adults is influenced by the time of day in which they are tested. It has been suggested (May, Hasher, & Zacks, 1993) that some of the reported age differences in performance may be attenuated when older adults are tested during their optimal time, and younger adults are tested during their nonoptimal time. A total of 100 adults (20 to 78 years of age) participated in this study to investigate whether time of day and/or age are significant predictors of cognitive performance. Three tasks measuring crystallized and fluid types of abilities were employed. Hierarchical regression analyses revealed that age was a significant predictor for two of the tasks, whereas time of day of testing did not predict performance for any of the three types of tasks. The results suggest that time of day influences may be limited to specific types of cognitive abilities.