The Reliability of Performance of Healthy Adults on Three Visual Perception Tests

Beginning of article

Problems with visual perceptual skills have been shown to have a negative impact on the daily living skills of individuals and are, therefore, commonly assessed by occupational therapists. The purpose of this study was to examine two types of reliability (internal consistency and test-retest reliability) of three newly revised or developed adult visual perception tests. The participants were 50 healthy adults, aged 18 to 55 years, from Melbourne, Victoria, Australia. The participants completed the Developmental Test of Visual Perception--Adolescent and Adult (DTVP-A), the Motor-Free Visual Perception Test--Third Edition (MVPT-3) and the Test of Visual Perceptual Skills (non-motor)--Third Edition (TVPS-3). Internal consistency was examined using Cronbach's alpha calculations and test-retest

reliability was analysed using Spearman rho non-parametric correlation coefficients. The results indicated that the DTVP-A, the MVPT-3 and the TVPS-3 had total scale internal consistency correlation scores of 0.60 or higher (0.60, 0.69 and 0.63 respectively). The majority of the subscales of each test had lower correlation coefficients than the overall scores (ranging from 0.22 to 0.49). For the DTVP-A, MVPT-3 and TVPS-3 total scale scores, the test-retest reliability correlation coefficients were statistically significant (rho = 0.46, p<0.05; rho = 0.62, p<0.01; and rho = 0.59, p<0.01, respectively). Overall, the three visual perceptual tests exhibited low to moderate levels of internal consistency and test-retest reliability.

Key words: Visual perception, assessment, occupational therapy, internal consistency, test-retest reliability.

Introduction

Occupational therapists frequently assess the visual perceptual abilities of adult clients since problems with visual perception have been shown to have a negative impact on the daily living skills of individuals (Cockburn et al 1990, Edmans et al 1991, Connor and Padula 2005). Visual perceptual dysfunction is commonly associated with clinical conditions involving a neurological disorder or an acquired injury, such as a cerebrovascular accident (Barer et al 1990, Jesshope et al 1991, Cherney et al 2001, Mercier et al 2001, Donnelly 2002), acquired brain injury (Neistadt 1990), dementia (Hill et al 1995, Glosser et al 2002), cerebral palsy (Bouska et al 1990), Parkinson's disease (Bouska et al 1990) or multiple sclerosis (Unsworth 1999). Therefore, occupational therapists often assess the visual perceptual skills of adults presenting with a neurological impairment.

Accuracy in the assessment of visual perception is dependent on the tests used by professionals possessing sound measurement properties, such as reliability. If an instrument has well established levels of reliability, professionals can use the test with confidence because it will provide a consistent and stable measure of clients' abilities, with little random error or influence from external factors (Benson and Schell 1997, Harris 2004, Richardson 2005, Kielhofner and Fossey 2006).

Three visual perceptual tests used with adults are the Developmental Test of Visual Perception--Adolescent and Adult (DTVP-A) (Reynolds et al 2002); the Motor-Free Visual Perception Test--Third Edition (MVPT-3) (Colarusso and Hammill 2003); and the Test of Visual Perceptual Skills (non-motor)--Third Edition (TVPS-3) (Martin 2006). The DTVP-A, the MVPT-3 and the TVPS-3 are all newly revised or developed motor-free tests of visual perception, with limited data published about their reliability (Busch-Rossnagel 1985, Denison 1985, Ryan 1988, Tindal 1995, Burtner et al 1997, Van Deusen and Brunt 1997, Volpe-Johnstone 2001, Asher 2007).

All three visual perceptual tests were originally developed for use with children and were subsequently standardised for use with adults. The DTVP-A is an adolescent and adult version of the Developmental Test of Visual Perception, 2nd edition (Hammill et al 1993). The MVPT-3 is a third edition and revision of the Motor-Free Visual Perception Test--Revised (Colarusso and Hammill 1996), with extended norms to include adults. The TVPS-3 is a combination of the Test of Visual Perceptual Skills (Non-Motor)--Revised (Gardner 1996) and the Test of Visual Perceptual Skills (non-motor) (Upper Level)--Revised (Gardner 1997).

The DTVP-A, the MVPT-3 and the TVPS-3 were all standardised in the United States, hence no research has been conducted about their use in cross-cultural contexts. The aim of this study was to investigate two types of reliability, internal consistency and test-retest reliability, of the DTVP-A, the MVPT-3 and the TVPS-3 in a cross-cultural setting. For the DTVP-A, only its three motor-reduced subscales (Figure-Ground, Visual Closure and Form Constancy) were included in this study.

The rationale for investigating the internal consistency and test-retest reliability of the DTVP-A, the MVPT-3 and the TVPS-3 was threefold. In the first instance, these three visual perceptual tests are all relatively new tests and, as such, no other reliability studies (other than those reported in the test manuals) involving them have been completed to date. Secondly, all three tests were developed in the United States, hence investigating their reliability performance in another country would provide evidence of their clinical utility in cross-cultural contexts. Finally, it is important for tests to be evaluated by researchers other than the test's author since this allows a body of knowledge about the test's psychometric properties to be generated. It is important for tests to be peer reviewed and peer evaluated because this provides both valuable information to inform prospective test users and objective information about tests' reliability and validity. Further, critiques of previous versions of the tests have also recommended that their psychometric properties be evaluated by external groups (Busch-Rossnagel 1985, Denison 1985, Ryan 1988, Tindal 1995, Burtner et al 1997, Brown et al 2003a, 2003b).

Literature review

Visual perception

Visual perception is a dynamic process, whereby information is received through sensory impulses and translated into meaning, based on a previously developed view of the environment (Cooke et al 2006). The total process involves the extraction and organisation of visually perceived stimuli from the environment and the cognitive processes required for the interpretation of what is seen (Schneck 2005). Visual perception results in the functional vision required for active involvement in daily living, including independence in self-care tasks and participation in educational, work or leisure activities (Erhardt and Duckman 1997, Scheiman 1997). Visual perceptual skills measured by the DTVP-A, the MVPT-3 and the TVPS-3 have been categorised into five subtypes, representing the theoretical constructs of visual perception: visual discrimination, spatial relationships, visual memory, figure-ground and visual closure (Colarusso and Hammill 2003, Schneck 2005, Martin 2006).

Disorders of visual perception involve difficulty in perceiving and understanding the information received through the visual system as a result of a dysfunction in the cortex of the brain. Adults presenting with visual perceptual problems may experience difficulties with dressing, eating, reading, writing, mathematics, locating objects, keyboarding, reading a map, participating in leisure activities and /or driving (Brown et al 2003a, Ishihara et al 2004, Schneck 2005). These are skills required for completing everyday tasks, such as selecting a single required item from a number of items in a refrigerator or from a crowded shelf, or locating key information on a recipe, set of instructions, bill or map. Importantly, a person's safety may be at risk if he or she selects an incorrect item in the kitchen or bathroom (Kohlmeyer 2003). Visual perceptual abilities therefore need to be a greater area of focus for occupational therapists working with adults, particularly those who have experienced a neurological event or injury (Cockburn et al 1990, Titus et al 1991, Warren 1993a, 1993b, Connor and Padula 2005).

Test reliability

Tests used to assess visual perceptual skills are required to have well established measurement properties (such as reliability) to ensure accuracy and consistency in the assessment of visual perceptual abilities (American Educational Research et al 1999, Asher 2007). There are a number of types of reliability and they all have different uses. Reliability refers to how consistent and stable the results obtained with a particular test are when used under different circumstances or examining conditions as well as with different respondent groups …