Assessment of Cognitive Ability of Students with Severe and Low-Incidence Disabilities - Part 2

Article excerpt

The assessment of cognitive ability in students with the most severe disabilities presents a challenge to the clinicians who are charged with this task. This article is the second of a two-part series that summarizes what is currently known about effective assessment of the cognitive ability of students with significant impairments in order to improve service delivery to them. Part 1 presented background information and addressed assessment of cognitive ability in individuals with visual andhearing impairments. Part 2 summarizes the professional literature examining a variety of tests of cognitive ability that can be used with students with language impairments, motor impairments, and significant intellectual disabilities.

LANGUAGE IMPAIRMENTS

Language impairments can involve difficulty with grammar (syntax), vocabulary (semantics), the rules and system for speech sound production (phonology), units of word meaning (morphology), and the use of language, particularly in social contexts (pragmatics). Expressive language delays may exist without receptive language delay, but they can also co-occur in mixed expressive/receptive language disorders (American Speech-Language-Hearing Association, 1993).

As a consequence of the heavy verbal loading of most standardized cognitive assessments, children with severe language impairments are unable to be adequately assessed utilizing traditional cognitive assessment techniques. Indeed, research utilizing factor analyses has demonstrated that nearly 50% of the variance in children's performance on cognitive tests is accounted for by language abilities (Losch & Dammann, 2004), leaving little roomfor accurately assessing the cognitive ability of children with significant language impairments utilizing standard cognitive batteries. This is of particular concern for children with autism, especially those who are low functioning, as significant language deficits are inherent to the disorder. Research indicates that scores obtained from traditional measures of intelligence have underestimated the intellectual ability of children with autism spectrum disorders (see Edelson, 2006 for a review), perhaps because language deficits may be independent of cognitive ability (Dodd & Thompson, 2001; Lord & Paul, 1997). Thus, the use of measures of intelligence that take into account the interference of autism, particularly the significant language impairments, is of critical importance in identifying core cognitive impairments and for educational and treatment planning for this population.

For children with a lack of intelligible expressive communication because of profound articulation difficulties, the Leiter International Performance Scale-Revised (Leiter-R; Roid & Miller, 1997) or the Comprehensive Test of Nonverbal IntelligenceSecond Edition (CTONI-2; Hammill, Pearson, & Wiederholt, 2009) may be used (Quinn, 2010; Sattler, 2008). The Wechsler Nonverbal Scale of Ability (WNS; Wechsler & Naglieri, 2006) may also be considered (Sattler, 2008), although this assessment has less research supporting its use in populations with disabilities and may, in fact, not be a valid measure for children with any disability.

For both receptive and/or expressive language difficulties, the Universal Nonverbal Intelligence Test (UNIT; Bracken 8c McCallum, 1998) is an optimal choice, (Farrell 8c Phelps, 2000; Sattler, 2008). However, it is important to note that the UNIT has dated and consequently questionable norms. While matrices-based tests such as Raven's Progressive Matrices (Raven, Raven, 8c Court, 1998) and the Test of Nonverbal Intelligence (TONI-4; Brown, Sherbenou, 8c Johnsen, 2010) are often used with this population, these and other figural-reasoning tests should not be used in place of comprehensive measures of cognitive ability because they measure intelligence based on figure reasoning only. They should only be used as a screening measure of nonverbal ability (Sattler 8c Hoge, 2006). …