Speed of processing in children with specific language impairment.

The aim of the present study was to investigate the speed with which children with specific language impairment (SLI) respond on a range of tasks. Seventy-seven third-grade children participated in 10 different tasks (involving a total of 41 conditions), including nonlinguistic and linguistic activities. Mean response times (RTs) of children with SLI (n = 29) increased as a function of mean RTs of children with normal language (NLD, n = 29) under each of three different regression models; children with SLI responded more slowly across all task conditions, and also when linguistic and nonlinguistic tasks were analyzed separately. Children with nonspecific language impairment (NLI) were also included (n = 19). The results were similar to those for children with SLI, but the degree of slowing was greater. The results of the group analyses support the hypothesis that speed of processing in children with SLI is generally slower than that of children with normal language. However, some children with SLI do not appear to show deficits of this type.

Distinguishing short-term memory from working memory.

The aim of the present research was to determine whether short-term memory and working memory could be distinguished. In two studies, 7- to 13-year-olds (N = 155, N = 132) were administered tasks thought to assess short-term memory as well as tasks thought to assess working memory. Both exploratory and confirmatory factor analyses distinguished short-term memory tasks from working memory tasks. In addition, performance on working memory tasks was related to word decoding skill but performance on short-term memory tasks was not. Finally, performance on both short-term memory and working memory tasks were associated with age-related increases in processing speed. Results are discussed in relation to models of short-term and working memory.

Brief report: speed of information processing in children with insulin-dependent diabetes mellitus.

OBJECTIVE: To determine whether children with insulin-dependent diabetes mellitus (IDDM) process information more slowly than children who do not have diabetes. METHODS: We tested 31 children with early onset and longer duration of IDDM, 35 with later onset and briefer duration of IDDM, and 36 comparison children without diabetes. They were administered five tasks requiring rapid responding that assessed a range of cognitive processes. RESULTS: On most tasks, children in the three groups were quite similar in the accuracy and speed of performance. Furthermore, for children in the diabetic groups, disease-related variables were unrelated to accuracy and speed of performance. CONCLUSIONS: The results suggest that children with IDDM do not have a pervasive deficit in speed of information processing, although more circumscribed deficits in processing speed are possible.

Speed of information processing in patients with multiple sclerosis.

To determine the extent to which multiple sclerosis (MS) slows cognitive processes, speeded tasks were administered to 11 patients with MS and to 11 comparison subjects without MS. On all tasks, patients with MS responded more slowly than comparison subjects. More important, response times (RTs) for patients with MS increased systematically as a function of RTs for comparison subjects, and the increase was best described by a power function. These data are consistent with the view that MS produces a general slowing of cognitive processes, and with the view that the cognitive slowing associated with aging reflects neural noise.

Phonological skill and articulation time independently contribute to the development of memory span.

One hundred twenty 6- to 10-year-olds were administered three measures of speed of processing, three memory span tasks, three tasks assessing phonological skill, and three articulation tasks assessing the speed with which they could say familiar stimuli aloud. Regression analyses revealed that performance on the span tasks was predicted by performance on the phonology and articulation tasks but not by age or performance on the processing speed tasks. Results are discussed in terms of the processes responsible for age-related change in memory span.

Processing time, imagery, and spatial memory.

Measures of cognitive processing time, imagery skill, and spatial memory span were administered to 128 8- to 20-year-olds. Age correlated positively with spatial memory span and accuracy on the imagery tasks but negatively with times on the cognitive processing and imagery tasks. Results of path analyses and structural-equation modeling were consistent with a causal model in which age-related change in speed of processing is associated with more effective imagery. In turn, imagery is associated with spatial memory span. Age was also associated with imagery and spatial span, indicating that other age-related variables need to be incorporated into the causal model.

Short-term memory and strategy use in children with insulin-dependent diabetes mellitus.

The present study was designed to examine recall and rehearsal in short-term memory among children with insulin-dependent diabetes mellitus (IDDM). Children with onset of IDDM before age 5 years, children with onset after 5 years, and children without IDDM were administered a measure of short-term memory that provides information about rehearsal as well as level of recall. Children with later onset of diabetes and children without IDDM were expected to recall more words and use more effective rehearsal strategies than children with early onset of diabetes. Results indicate that children diagnosed with IDDM early in life used similar rehearsal strategies but recalled fewer words than children with later onset of diabetes and children without IDDM. In addition, results provide evidence that children who are in poor control of their diabetes did not use strategies designed to increase recall as often, or as well as, children in better control of their diabetes.

Processing speed as a mental capacity.

Throughout the lifespan, there are pronounced age differences in speed of processing, differences that are consistently related to performance on measures of higher-order cognition. In this article, we examine domain-specific and global explanations of these age differences in processing speed; we conclude that although experience can play a role in age differences in speed, there is also evidence that a general mechanism limits speeded performance. We also review research that shows the influence of processing speed on the quality of performance on nonspeeded tasks such as reasoning and memory. We suggest that speed of processing should be viewed as a fundamental part of the architecture of the cognitive system as it develops across the entire lifespan.

A method for studying the generalized slowing hypothesis in children with specific language impairment.

The present work was conducted to demonstrate a method that could be used to assess the hypothesis that children with specific language impairment (SLI) often respond more slowly than unimpaired children on a range of tasks. The data consisted of 22 pairs of mean response times (RTs) obtained from previously published studies; each pair consisted of a mean RT for a group of children with SLI for an experimental condition and the corresponding mean RT for a group of children without SLI. If children with SLI always respond more slowly than unimpaired children and by an amount that does not vary across tasks, then RTs for children with SLI should increase linearly as a function of RTs for age-matched control children without SLI. This result was obtained and is consistent with the view that differences in processing speed between children with and without SLI reflect some general (i.e., non-task specific) component of cognitive processing. Future applications of the method are suggested.

Processing time, articulation time, and memory span.

In each of two experiments, measures of memory span, processing time, and articulation time were administered. One study involved 7- to 14-year-olds and adults living in the United States (N = 288); the other, 7- to 12-year-olds and adults living in Korea (N = 84). In both studies, the natural logarithm of age was correlated positively with measures of memory span but negatively with measures of processing and articulation times. Causal modeling indicated that age-related change in processing time is associated with a decrease in the time required to articulate numbers and letters, which determines memory span.

Processing time decreases globally at an exponential rate during childhood and adolescence.

Children (N = 108) from 6 to 16 years of age and adults (N = 108) were tested on four speeded tasks that included 19 different experimental conditions. The 6- to 16-year-olds' response times (RTs) increased linearly as a function of adults' RTs in those same conditions. The slope of this linear function declined exponentially with age at a rate that could be predicted accurately from values established in previous research.

Evidence for global developmental change is intact.

In this article, I argue that most of the claims made by Morrison, Morrison, and Keating (1992) do not undermine the key results of the Kail (1988) study and that, contrary to their claims, the evidence still provides support for the original conclusion that a global mechanism is implicated in age-related change in speed of processing.

General slowing of information-processing by persons with mental retardation.

On measures of speeded performance, persons with mental retardation typically respond more slowly than do those without mental retardation. A review of 45 published studies yielded 518 pairs of response times (RTs) in which each pair consisted of a mean RT for a group of persons with mental retardation for an experimental condition and the corresponding mean RT for a group of persons without mental retardation. The primary result was that RTs of individuals with mental retardation increased linearly as a function of RTs for persons without mental retardation in corresponding conditions. These results are consistent with the view that differences in processing speed between persons with and without mental retardation reflect some general (i.e., nontask specific) component of cognitive processing. Possible candidates for the general component were discussed.

Controlled and automatic processing during mental rotation.

In two experiments, 9- and 10-year-olds and adults were tested on a mental rotation task in which they judged whether stimuli presented in different orientations were letters or mirror-images of letters. The mental rotation task was performed alone on 48 trials and concurrently with a memory task on 48 additional trials. The concurrent memory task in Experiment 1 was recalling digits; in Experiment 2, recalling positions in a matrix. The key result was that the slope of the function relating response time to stimulus orientation was the same when the mental rotation task was performed alone and when performed concurrently with the memory task. This result is interpreted as showing that mental rotation is an automatic process for both children and adults.

Developmental change in speed of processing during childhood and adolescence.

Throughout childhood and adolescence, there are consistent age differences in speed of processing. Here 72 published studies yielded 1,826 pairs of response times (RTs) in which each pair consisted of adults' mean RT for a condition and the corresponding mean RT for a younger group. The primary results were that (a) children's and adolescents' RTs increase linearly as a function of adult RTs in corresponding conditions and (b) the amount of increase becomes smaller with age in a manner that is well described by an exponential function. These results are consistent with the view that age differences in processing speed reflect some general (i.e., nontask specific) component that changes rapidly during childhood and more slowly during adolescence. Possible candidates for the general component are discussed.

Impact of practice on speed of mental rotation.

We tested 11- and 20-year-olds on 3360 trials of a mental rotation task in which they judged if stimuli presented in different orientations were letters or mirror images of letters. Children's and adults' processing times decreased substantially over practice. These changes were well characterized by hyperbolic and power functions in which most of the parameters of those functions were constrained to adults' values. Performance on two transfer tasks, mental rotation of letter-like characters and memory search for numbers, indicated that the practiced skill did not generalize to other domains. The results are discussed in terms of different mechanisms that might be responsible for the impact of practice.

Morphology of single, physiologically identified retinogeniculate Y-cell axons in the cat following damage to visual cortex at birth.

It has been reported previously that neurons in the dorsal lateral geniculate nucleus (LGN) of cats with neonatal damage to visual cortex (KVC cats) have receptive fields that are abnormally large and that the receptive fields of these neurons sometimes do not appear to conform to the normal retinotopic order in the LGN. A primary aim of this study was to determine if these physiological abnormalities are related to inappropriate patterns of retinogeniculate connections. We therefore have analyzed the terminal arbors of retinogeniculate axons in adult cats that had received a lesion of visual cortex (areas 17, 18, and 19) on the day of birth. Single retinogeniculate axons were characterized physiologically and injected intracellularly with horseradish peroxidase. Consistent with earlier reports that neonatal removal of visual cortex results in a retrograde loss of retinal X-cells, all of the retinogeniculate axons that we recorded were from Y-cells. While the visual responses of these Y-cell axons were normal, the morphology of their terminal arbors in the LGN was abnormal. Retinal Y-cell axons in KVC cats have terminal fields in the A laminae of the LGN that are as large or larger than those of normal Y-cells. However, since the LGN in KVC cats is severely degenerated, single Y-cell arbors occupy a proportional volume of the LGN that is 12 times greater than normal. Thus an early lesion of visual cortex produces a severe mismatch between retinogeniculate axon arbor size and target size. Also, despite the normal size of retinogeniculate axon arbors in KVC cats, the number and density of terminal boutons are greatly decreased. Thus our morphological results suggest that the unusually large receptive fields of LGN cells in KVC cats and the relative lack of retinotopic precision in the LGN are due, at least in part, to anomalies in the relative size and distribution of retinogeniculate axon arbors that develop after neonatal removal of visual cortex.

Reply to Stigler, Nusbaum, and Chalip.

In this article, I show that many of Stigler et al.'s criticisms of my 1986 article are incorrect or based on assumptions that are implausible. I agree with their conclusion, however, that theories of cognitive development must include both domain-specific and general processes.

Developmental functions for speeds of cognitive processes.

In Experiment 1, 8- to 21-year-olds were tested on a visual search task in which they determined whether a target digit was present in a set of one to five digits and a memory search task in which they determined whether a target digit was a member of a previously presented set of one to five digits. Increases with age in speeds of visual and memory search were both described well by exponential functions, and the rate of developmental change was similar for the two processes. In Experiment 2, 8- to 22-year-olds were tested on a memory search task, a mental rotation task in which they judged whether a stimulus presented in various orientations was a letter or a mirror image of a letter, an analogical reasoning task in which they judged whether sets of pictures were related to one another according to the same rule, and a mental addition task in which they judged the accuracy of problems such as 2 + 3 = 6. Here, too, for three of the four tasks developmental change was described well by exponential functions with a common rate of change. Results are interpreted in terms of a central mechanism that limits speeded performance and that changes with age.