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.

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.

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.

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.

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.

Phasic alertness and differences in picture encoding speed.

The relation between physical identity and name identity encoding speed was assessed. Correlational analyses indicated that similar processes may be involved in the two types of encoding and, by implication, that differences between mentally retarded and nonretarded subjects' physical identity and name identity encoding speed may result from common factors. Also, we assessed the extent to which differences in preparation for the presentation of external stimuli may account for any observed differences in encoding speed. A difference between retarded and nonretarded subjects in preparation time was apparent; however, this difference did not influence encoding speed.

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.