Personality traits predict attitudes toward individuals with intellectual disability

Background: Explaining individual differences in people's attitudes toward individuals with intellectual disability (ID) is important for increasing social inclusion of people with ID. The aim of the current study was to replicate and extend past research by formulating a single model of attitudes toward individuals with ID with several predictors: personality traits, quality and quantity of contact, perceived knowledge of ID, social desirability, and demographics. Methods: A sample of 221 undergraduate students in the United States completed several surveys in a lab setting: the Mental Retardation Attitude Inventory-Revised, the Big Five Inventory, McManus et al.'s measures of contact with and perceived knowledge of ID, and the Marlowe-Crowne Social Desirability Scale. Results: Results replicated previous findings by showing quality of contact was the strongest predictor of attitudes. Additionally, we found openness to experience and agreeableness remained significant predictors after holding all other variables constant. A follow-up mediation analysis demonstrated that quality of contact mediated the relations from openness and agreeableness to attitudes. Conclusions: Findings suggest personality factors can influence attitudes toward individuals with ID, and further emphasize the importance of quality of contact. Implications for the social inclusion of individuals with ID are discussed.

The Acquisition of Survey Knowledge by Individuals With Down Syndrome

People with Down syndrome often exhibit deficiencies in wayfinding activities, particularly route learning (e.g., Courbois et al., 2013; Davis et al., 2014; Farran et al., 2015). Evidence concerning more sophisticated survey learning has been sparse. In the research reported here, two experiments are reported that evaluated survey learning of youth with DS and typically developing children (TD) matched on mental age. In Experiment 1, participants learned two overlapping routes consisting of three turns each through a virtual environment depicting 9 square city blocks. Following acquisition, they were tested on multiple measures of survey knowledge: finding a shortcut, identifying the direction of landmarks not currently visible from their location in the environment, and recognizing a bird's-eye representation of the overall environment. Under these conditions, which should provide relatively optimal opportunities for survey learning, the participants with DS performed comparably to TD participants matched on non-verbal ability on all of our measures of survey learning. Hence, we concluded that people with DS can acquire some survey knowledge when tasked with learning a small environment and given the opportunity to do so. In Experiment 2, the experimenter navigated participants through a large, relatively complex, virtual environment along a circuitous path, beginning and ending at a target landmark. Then, the participants were placed at a pre-specified location in the environment that they had viewed previously and instructed to navigate to the same target (a door) using the shortest possible path from their current location. They completed the task three times: once after being shown the environment one time, once after three exposures, and once after five exposures. Results indicated that the participants with DS exhibited significantly less skill at identifying the shortcut than did the TD participants, with differences emerging as the number of exposures increased. Participants with DS were also less able to recall landmarks at the end of the experiment. Overall, however, the performance of both groups was relatively poor in both experiments - with the performance of participants with DS being worse as conditions became less optimal. These results were discussed in terms of underlying mechanisms that may account for variations in survey learning as environmental complexity increases.

Growth and Decline in Language and Phonological Memory Over Two Years Among Adolescents With Down Syndrome

Forty-two adolescents with Down syndrome (DS) ages 10 to 21 years completed a battery of language and phonological memory measures twice, 2 years apart. Individual differences were highly stable across two years. Receptive vocabulary scores improved, there was no change in receptive or expressive grammar scores, and nonword repetition scores declined. Digit memory and expressive vocabulary scores improved among younger adolescents, but generally held steady among older adolescents. These patterns may reveal key points in development at which interventions may be best applied. Further research is needed to understand specific processes in tasks that appear to be slowing or declining during adolescence. They may be important for understanding early aging and dementia in DS.

Implicit memory of locations and identities: A developmental study

Objects in the environment have both location and identity properties. However, it is unclear how these independent properties are processed and combined in the implicit domain. The current study investigated the development of the implicit memory of object locations and object identities, both independently and combined, and the relation between implicit memory and working memory (WM) for these properties. Three age groups participated: 6- and 7-year-old children, 9- and 10-year-old children, and adults. Children and adults completed a repeated search paradigm. In the learning phase, targets' locations were consistently predicted by both the identities and locations of the distracters. In the test phase, either both remained predictive or just the identities or just the locations of the distracters predicted the location of the target. All groups showed significant implicit learning when both the identities and locations of the distracters remained predictive. When only the locations but not the identities of the distracters were predictive, adults and 9- and 10-year-olds showed significant learning, whereas 6- and 7-year-olds did not. When only the identities but not the locations of the distracters were predictive, none of the groups showed significant learning effects. In evaluating the contributions of either visual or spatial WM to implicit learning and memory, we found that children with smaller visual WM exhibited larger implicit memory effects for object identities than did children with larger visual WM. Taken together, the results indicate that children's ability to differentiate identity and location undergoes development even in the implicit domain.

Sex Differences in Using Spatial and Verbal Abilities Influence Route Learning Performance in a Virtual Environment: A Comparison of 6- to 12-Year Old Boys and Girls

Previous studies have reported sex differences in wayfinding performance among adults. Men are typically better at using Euclidean information and survey strategies while women are better at using landmark information and route strategies. However, relatively few studies have examined sex differences in wayfinding in children. This research investigated relationships between route learning performance and two general abilities: spatial ability and verbal memory in 153 boys and girls between 6- to 12-years-old. Children completed a battery of spatial ability tasks (a two-dimension mental rotation task, a paper folding task, a visuo-spatial working memory task, and a Piagetian water level task) and a verbal memory task. In the route learning task, they had to learn a route through a series of hallways presented via computer. Boys had better overall route learning performance than did girls. In fact, the difference between boys and girls was constant across the age range tested. Structural equation modeling of the children’s performance revealed that spatial abilities and verbal memory were significant contributors to route learning performance. However, there were different patterns of correlates for boys and girls. For boys, spatial abilities contributed to route learning while verbal memory did not. In contrast, for girls both spatial abilities and verbal memory contributed to their route learning performance. This difference may reflect the precursor of a strategic difference between boys and girls in wayfinding that is commonly observed in adults.

Response cost to repeated displays--when previous distractors become targets

A varied-target search task was used to evaluate the response cost of previous distractors becoming current targets in repeated visual search. We compared the relative contributions of distractor identity and location to producing response cost. During an exposure phase, half of the items were possible targets in each repeated display, and the other half were always distractors. Participants searched for a different target from the set of potential targets when the search displays were repeated. In the test phase of Experiments 1a and 1b, the roles of targets and distractors were reversed while the overall configuration was unchanged. Results indicated significant contextual costs after the switch of identities/locations between distractors and targets. In the test phase of Experiments 2a and 2b, target identities were changed again but the target locations remained the same. Less response cost was observed in this condition relative to when both identities and locations were changed. Proximity between target and distractors in the repeated displays also influenced response cost. The mechanisms responsible for the various response cost effects and the interplay between identity, location, and proximity in the production of response cost were discussed.

Age-related similarities in contextual cueing in the presence of unpredictive distracters

Contextual cueing effects of 6-8-year-old children, 10-12-year-old-children, and college students were compared under conditions in which some of the distracters in the search displays predicted the location of the target and other distracters did not. More specifically, the percent of distracters that predicted the location of the target varied across three conditions (100%, 67%, and 33%). Previous research had indicated that children are impacted more than adults when the percent of predictive distracters is relatively low. However, that research included new displays as well as repeated displays as participants were implicitly learning the association between the predictive distracters and the target. This re-evaluation did not introduce new display until a separate test phase. Results suggested that all three age groups demonstrated significant and comparable contextual cueing effects across all three signal-to-noise ratio conditions. Hence, children appear to possess the general ability to extract and remember information associated with spatial regularities in the presence of considerable spatial noise. In addition, contextual cueing effects were linked to improvements in search efficiency for all groups in this study, providing another degree of similarity across variations in age.

Patterns of differences in wayfinding performance and correlations among abilities between persons with and without Down syndrome and typically developing children

Down syndrome (DS) impacts several brain regions including the hippocampus and surrounding structures that have responsibility for important aspects of navigation and wayfinding. Hence it is reasonable to expect that DS may result in a reduced ability to engage in these skills. Two experiments are reported that evaluated route-learning of youth with DS, youth with intellectual disability (ID) and not DS, and typically developing (TD) children matched on mental age (MA). In both experiments, participants learned routes with eight choice point presented via computer. Several objects were placed along the route that could be used as landmarks. Participants navigated the route once with turn indicators pointing the way and then retraced the route without them. In Experiment 1 we found that the TD children and ID participants performed very similarly. They learned the route in the same number of attempts, committed the same number of errors while learning the route, and recalled approximately the same number of landmarks. The participants with DS performed significantly worse on both measures of navigation (attempts and errors) and also recalled significantly fewer landmarks. In Experiment 2, we attempted to reduce TD and ID vs DS differences by focusing participants’ attention on the landmarks. Half of the participants in each group were instructed to identify the landmarks as they passed them the first time. The participants with DS again committed more errors than the participants in the ID and TD groups in the navigation task. In addition, they recalled fewer landmarks. While landmark identification improved landmark memory for both groups, it did not have a significant impact on navigation. Participants with DS still performed more poorly than did the TD and ID participants. Of additional interest, we observed that the performance of persons with DS correlated with different ability measures than did the performance of the other groups. The results the two experiments point to a problem in navigation for persons with DS that exceeds expectations based solely on intellectual level.

The acquisition of contextual cueing effects by persons with and without intellectual disability

Two experiments were conducted to compare the acquisition of contextual cueing effects of adolescents and young adults with intellectual disabilities (ID) relative to typically developing children and young adults. Contextual cueing reflects an implicit, memory based attention guidance mechanism that results in faster search for target locations that have been previously experienced in a predictable context. In the study, participants located a target stimulus embedded in a context of numerous distracter stimuli. During a learning phase, the location of the target was predictable from the location of the distracters in the search displays. We then compared response times to locating predictable relative to unpredictable targets presented in a test phase. In Experiment 1, all of the distracters predicted the location of the target. In Experiment 2, half of the distracters predicted the location of the target while the other half varied randomly. The participants with ID exhibited significant contextual facilitation in both experiments, with the magnitude of facilitation being similar to that of the typically developing (TD) children and adults. We concluded that deficiencies in contextual cueing are not necessarily associated with low measured intelligence that results in a classification of ID.

Visuo-spatial ability in individuals with Down syndrome: is it really a strength?

Down syndrome (DS) is associated with extreme difficulty in verbal skills and relatively better visuo-spatial skills. Indeed, visuo-spatial ability is often considered a strength in DS. However, it is not clear whether this strength is only relative to the poor verbal skills, or, more impressively, relative to cognitive ability in general. To answer this question, we conducted an extensive literature review of studies on visuo-spatial abilities in people with Down syndrome from January 1987 to May 2013. Based on a general taxonomy of spatial abilities patterned after Lohman, Pellegrino, Alderton, and Regian (1987) and Carroll (1993) and existing studies of DS, we included five different domains of spatial abilities - visuo-spatial memory, visuo-spatial construction, mental rotation, closure, and wayfinding. We evaluated a total of 49 studies including 127 different comparisons. Most comparisons involved a group with DS vs. a group with typical development matched on mental age and compared on a task measuring one of the five visuo-spatial abilities. Although further research is needed for firm conclusions on some visuo-spatial abilities, there was no evidence that visuo-spatial ability is a strength in DS relative to general cognitive ability. Rather, the review suggests an uneven profile of visuo-spatial abilities in DS in which some abilities are commensurate with general cognitive ability level, and others are below.

Contextual cueing effects across the lifespan

The authors evaluated age-related variations in contextual cueing, which reflects the extent to which visuospatial regularities can facilitate search for a target. Previous research produced inconsistent results regarding contextual cueing effects in young children and in older adults, and no study has investigated the phenomenon across the life span. Three groups (6, 20, and 70 years old) were compared. Participants located a designated target stimulus embedded in a context of distractor stimuli. During exposure, the location of the target could be predicted from the location of the distracters in each display. During test, these predictable displays were intermixed with new displays that did not predict the target location. Response times to locating predictable relative to unpredictable targets were compared. All groups exhibited facilitation effects greater than 0 (95% CIs [.02, .11], d = .4; [.01, .12], d = .4; and [.01, .10], d = .4, for the children, young adults, and older adults, respectively) indicating that contextual cueing is robust across a wide age range. The relative magnitude of contextual cueing effects was essentially identical across the age range tested, F(2, 103) = 1.71, eta rho2 = .02. The authors argue that a mechanism that uses environmental covariation is available to all age ranges, but the expression of the contextual cueing may depend on the way it is measured.

Asymmetry and performance: Toward a neurodevelopmental theory

Hemispheric asymmetry implies the existence of developmental influences that affect one hemisphere more than the other. However, those influences are poorly understood. One simple view is that asymmetry may exist because of a relationship between a mental process' degree of lateralization and how well it functions. Data scaling issues have largely prevented such investigations, but it is shown that scaling effects are minimized after correction for ceiling and floor effects. After correction, lateralization-performance correlations are pervasive. However, while some correlations are positive, others are negative, with the direction depending on the underlying lateralized process. Two hypotheses are proposed that can account for these relationships by pointing either to individual differences in maturation of the corpus callosum or to developmental limits encountered at different ages of childhood. Their investigation should contribute toward a neurodevelopmental theory of hemispheric asymmetry.

Inhibition of return and negative priming by persons with and without mental retardation

Persons with and without mental retardation who were matched on CA took part in three tasks: an inhibition of return task, a location negative-priming task, and an identity negative-priming task. Having participants perform all three tasks allowed us to correlate performance among the tasks and assess the various relationships among performance measures on negative priming and inhibition of return. The participants with mental retardation did not exhibit negative priming of identity. However, they did exhibit negative priming of location and inhibition of return. The participants without mental retardation exhibited all three effects. A different pattern of correlations was observed for the participants with and those without mental retardation. Possible reasons for this difference are discussed.

Interference and Inhibition in Tasks of Selective Attention by Persons With and Without Mental Retardation

Persons with mental retardation often exhibit greater interference in visual selective attention tasks than do persons matched with them on CA. My goal here was to evaluate whether differences in distractor interference between persons with and without mental retardation may be related to differences in negative priming. Fifteen participants with mental retardation, 15 without mental retardation matched on CA, and 15 without mental retardation matched on MA participated in three selective attention tasks, which were chosen to elicit small, medium, and large group differences in interference, respectively. The failure to engage in inhibitory processes by the participants with mental retardation in these tasks of selective attention was related to increased distractor interference.

Preattentive Orienting in Adolescents With Mental Retardation

Visual attention is preattentively drawn to abrupt onsets of stimuli appearing in a visual array. In this experiment, I examined the speed of attentional capture for persons with and without mental retardation. Participants identified target stimuli that were signaled by a valid location cue (20% of the time), an invalid location cue (60% of the time), or no cue (20% of the time). Participants without mental retardation exhibited maximum influence of the cue at cue/target separations that were 100 msec shorter than did participants with mental retardation. These results indicate that processing-speed differences between persons with and those without mental retardation can be observed even when processing resources not involved in the information processing.

Consistent mapping and automatic visual search: comparing persons with and without intellectual disability

BACKGROUND

Merrill et al. (1996) reported that persons with intellectual disability (ID) were slower at learning a visual search task to automaticity relative to persons of the same age without ID. For persons without ID, automaticity develops most rapidly under conditions in which a response is always the same for a particular stimulus. This study was designed to investigate whether persons with and without ID are differentially sensitive to the influence of consistently mapped versus inconsistently mapped stimulus responses.

METHODS

The primary manipulation was the consistency between a particular stimulus and the response to that stimulus in a visual search task. Sixteen participants with ID and 16 without ID searched displays of two, three, or four pictured objects to determine if a target was present. For half of the participants, the targets were always targets. For the other half, the targets became nontargets on 25% of the trials.

RESULTS

Analyses focused on changes in response times associated with set size. Because automaticity allows for parallel processing, the elimination of significant effects of set size was taken as an index of the development of automaticity. Results indicated that inconsistent mapping significantly slowed the development of automaticity for the participants without ID but not for the participants with ID.

DISCUSSION

Results were discussed in terms of the role of inhibition processes in the development of automatic search and detection. The effectiveness of inhibition processes was compromised by the consistency manipulation. The effect of the consistency manipulation was greater for the participants without ID because they were presumed to be using inhibition processes more effectively during practice than did the participants with ID.

Selective search for conjunctively defined targets by children and young adults

Two experiments were conducted to investigate age-related differences in visual search for targets defined by the conjunction of two features. In the experiments, 7- and 10-year-old children and young adults searched visual displays for a black circle among distractors consisting of gray circles and black squares. In Experiment 1 (N = 60), we compared performance in the standard search task (where an equal number of each type of distractor appeared across all display sizes) with performance in a modified search task (where the number of black squares was fixed at two and the number of gray circles increased as the display size increased). In Experiment 2 (N = 60), the ratio of black stimuli to gray stimuli was varied systematically as the display size increased. Results of both experiments indicated that all participants were able to restrict search to an appropriate subset of the display rather than conduct an exhaustive search. However, the young adults were more efficient in their ability to do so than were either the 7- or 10-year-old participants. The 10-year-olds were as efficient as the young adults when the number of black stimuli in the display was relatively small. However, these children became relatively less able to restrict search effectively as the number of black stimuli increased. Discussion focused on possible preattentive and attentive processes that may change systematically with age.

Implicit and explicit learning in young adults with mental retardation

We examined intelligence-related differences in explicit and implicit learning using an artificial grammar paradigm. Young adults with and without mental retardation completed a sequence-learning and identification task. For some participants, sequences were constructed following an artificial grammar; for others, sequences were random. Explicit learning was determined by ability to learn and later identify random sequences. Implicit learning was determined by the tendency to incorrectly identify new grammatical sequences as seen before, relative to new nongrammatical sequences. Participants with mental retardation did more poorly than participants without mental retardation on explicit learning but just as well on implicit learning. Results suggest that learning of complex materials, when accomplished through implicit processing, is functionally equivalent in individuals with and without mental retardation.

Similarities in negative priming between persons with and those without mental retardation of equal chronological age

Adolescents with and those without mental retardation participated in a negative priming procedure in two experiments. They identified letters to stimulus displays presented in pairs. Negative priming was observed as the slowing of response times when the distractor in the first display (prime) became the target in the second display (probe). In the standard procedure, all displays include one target and one distractor. In our modification, prime displays occasionally included a distractor without a target. Although adolescents with mental retardation typically do not exhibit negative priming when responding on the basis of stimulus identity, they did so with single letter primes in these experiments.

Negative priming and mental retardation: the processing of distractor information

Negative priming was assessed to investigate what information persons with and without mental retardation access from distractors. Subjects viewed displays of one blue and one red letter and were instructed to identify the blue letter. A prime display followed a probe display at intervals varying from 100 to 500 msec. At the short time interval, all subjects exhibited facilitation to identifying targets in the probe that were the same as the target or distractor of the prime, indicating the automatic activation of both letters. At the long interval, only the subjects without mental retardation exhibited inhibition of the distractors. The subjects with mental retardation did not suppress responding to the distractor to facilitate their performance.

Mental retardation and the acquisition of automatic processing

The acquisition of automatic processing in persons with and without mental retardation was examined. In Experiment 1, subjects viewed slides of objects to determine whether a pictured object belonged to a designated target category. There was an effect of search set size for both groups that decreased and eventually disappeared with practice. This result reflected the acquisition of automatic processing. Also, evidence of automaticity was observed with less practice for subjects without relative to subjects with mental retardation. In Experiment 2, subjects searched for the presence of a designated target shape in arrays containing two, three, or four shapes. Results were essentially the same. Implications of these results for the development of cognitive skills by persons with mental retardation were discussed.

Suppression of irrelevant location information by individuals with and without mental retardation

Negative priming in a location task was examined for individuals with and without mental retardation. In each prime display, a target stimulus was presented in one of four locations, with a distractor stimulus appearing in another location. The target in the probe appeared either in the same position as the target in the prime, the same position as the distractor, or a different position from both. In contrast to results obtained using identification tasks (Cha & Merrill, 1994), all subjects exhibited interference to locating the target in the negative priming condition. All individuals apparently actively suppressed response tendencies to the location of irrelevant information in the prime display.

Allocation of attention and task difficulty

Individuals with and without mental retardation did a dual task procedure designed to investigate how task difficulty influenced the allocation of attention. The primary task required semantic category decisions. Subjects sorted cards according to whether the object pictured on the card belonged to a target category. The easy decision task used basic level categories (horse and hammer). The difficult decision task used superordinate categories (animals and tools). While making decisions, subjects were required to signal detection of auditory probes. Response times to the probes were used to index attention to the primary task. Subjects without mental retardation allocated more attention to the difficult task. Those with mental retardation gave similar attention to the easy and difficult tasks. Possible explanations for their failure to allocate attention in accordance with task difficulty were discussed.

Facilitation and inhibition effects in visual selective attention processes of individuals with and without mental retardation

Adolescents with and without mental retardation participated in a visual selective attention task. They were required to identify one of two letters presented to them on the basis of color. We manipulated the relation between target and distractor letters on successive trials. A target letter could have been a target on the preceding trial, a distractor on the preceding trial, or not appear on the preceding trial. Subjects without mental retardation exhibited facilitation when the target was identical to the target on the preceding trial and inhibition when the target was a distractor on the preceding trial. Subjects with mental retardation also exhibited facilitation when the target was identical to the target on the preceding trial but not when it had been a distractor on the preceding trial. The inefficient suppression processes may result in performance deficits for individuals with mental retardation across a variety of tasks.

Sentence processing by adolescents with and without mental retardation

A more thorough test of the hypothesis that persons with mental retardation are less likely to construct semantically integrated representations of sentences that they hear than are subjects without mental retardation (Merrill & Bilsky, 1989; Merrill & Mar, 1987) was provided. A series of sentences were presented to adolescents with and without mental retardation. Their memory for the object nouns of the sentences was then tested when they were provided with either the subject noun, the verb, or the subject plus verb of the sentence as a retrieval cue. The two-word cue was relatively better if an integrated semantic representation was constructed. Manipulations included decreasing the processing time given to subjects (expected to inhibit the construction of integrated representations) and presenting a picture with the sentence (expected to facilitate the construction of integrated representations). The reduction in time decreased performance for the subjects without mental retardation to the level normally observed for those with mental retardation; presenting a picture increased performance of subjects with mental retardation to the level of comparison subjects. Results support the suggestion that previously observed differences in sentence processing between individuals with and without mental retardation may be due to differences in generating integrated representations of the sentences during processing.

Degree of associative relatedness and sentence processing by adolescents with and without mental retardation

Previous research has suggested that individuals with mental retardation are less likely than individuals without mental retardation to access and incorporate information about the relations between words of sentences in the representations of those sentences in memory (e.g., Merrill & Bilsky, 1990; Merrill & Jackson, in press). A cued recall study and a semantic verification study were conducted to determine whether the magnitude of this group difference could be made smaller by increasing the degree to which the words in the sentences were semantically related. In both experiments, individuals with mental retardation exhibited an ability to utilize contextual information to a greater extent when the words were related. In the highly related conditions, the differences between groups was virtually eliminated.

Attentional resource demands of stimulus encoding for persons with and without mental retardation

Speed of encoding differences between individuals with and without mental retardation were examined to determine whether they stem from an automatically executed cognitive process or from encoding processes that require attentional resources. In Experiment 1, encoding functions were generated for physical identity and name identity encoding while subjects retained a full memory load or half memory load. Size of memory load influenced encoding times for all subjects. However, the pattern of group differences suggested that subjects with mental retardation allocated fewer attentional resources to encoding, even though encoding may require more of their resources for efficient execution. These conclusions were supported in Experiment 2, in which resource allocation was assessed using response times to auditory probes placed at various locations in the semantic encoding and decision task.

Individual differences in the representation of sentences in memory

A cued recall procedure was used to assess the nature of the memory representation that underlies the ability of mentally retarded and nonretarded individuals to remember single sentences. Mentally retarded, equal-CA, and equal-MA subjects listened to a list of sentences after which their ability to recall the object noun of the sentence was assessed when they were provided recall cues that contained (a) only the subject noun of the original sentence, (b) only the verb of the sentence, or (c) both the subject and verb. As expected, performance for all groups was best when they were provided the subject plus verb cue relative to the single word cues. In addition, the groups differed in the magnitude of this two-word cue advantage, with the retarded subjects exhibiting the smallest and the equal-CA subjects exhibiting the largest advantage. This finding reflects a difference in the degree to which mentally retarded and nonretarded individuals construct sentence representations that more precisely specify the meaning of the sentence through the integration of its constituents.

Differences between mentally retarded and nonretarded persons' efficiency of auditory sentence processing

Mentally retarded adolescents and MA-matched nonretarded children participated in three experiments designed to examine differences in language-processing efficiency. A compressed speech technique was used in Experiments 1 and 2. Experiment 3 relied on a sentence-picture verification procedure. Our results suggest that retarded and nonretarded individuals differ in the speed with which they are able to execute the semantic-analytic processes but not necessarily the phonological encoding processes that are involved in auditory language comprehension. In addition, the data suggest a possible group difference in the quality of the semantic representation encoded during sentence processing.

Differences in semantic processing speed of mentally retarded and nonretarded persons

A modified Sternberg choice-reaction time procedure was used to compare differences in the speed with which mentally retarded and nonretarded adults were able to retrieve recently stored information from short-term memory and process permanently stored semantic information. Results revealed that the retarded adults were slower than were the nonretarded adults in both domains of processing; the relative magnitude of "processing inefficiency" exhibited by the retarded subjects was quite similar across the two domains (47% and 57% as efficient as the nonretarded subjects in short-term and long-term memory processing, respectively). This similarity suggests that inefficient processing may represent a fundamental deficiency of retarded individuals resulting from the inefficient execution of some central processing mechanism.