Ans. Neuropsychological assessment is incomplete without the visual and space perception (Warrington & James, 1991 as cited in Bonello et al., 1997). Visual object and space perception (VOSP) is a new measure of perception which aims to assess those skills which people who have suffered from a right hemisphere damage show deficits (Bonello et al., 1997). VOSP is made up of eight subtests (four of object perception and four of space perception), namely; shape detection, incomplete letters, silhouettes, object decision, dot counting, progressive silhouettes, position discrimination, number allocation and cube analysis (Warrington & James, 1991 as cited in Gorayska & Mey, 2004).
Advantages of VOSP
Brenda Rapp (2001) has stated that, “highly sophisticated methods of cognitive assessment can be developed if one uses as a starting point a detailed theory of relevant cognitive system” (Rapp, 2001, p.4). Good examples for theory based assessments methods for visual perception are Birmingham Object Recognition theory (BORB) (as given by Humphreys & Riddoch, 1993) and VOSP (Warrington & James, 1991). VOSP is made on Warrington’s model (Warrington & McCarthy, 1990 as cited in Lara et al., 2004). The model puts forward three subtypes of impaired object recognition. They are, “disorders of visual sensory discrimination” (Lara et al., 2004, p.386), apperceptive agnosia and associative agnosia. “Disorders of visual sensory discrimination reflect selective deficits affecting sensory processing including acuity, shape, discrimination and colour discrimination” (Lara et al., 2004, p.386), apperceptive agnosia is impaired object perception (Lara et al., 2004) and associative agnosia is when an individual is unable to derive meaning of the object presented despite having normal perceptual and sensory abilities(Lara et al., 2004). Thus, it can be inferred that object perception is not possible without object recognition in Warrington’s model (Lara et al., 2004) and it points out that object perception is an, “adequate integration of sensory, perceptual and representation information (Rapport, Millis & Bonello, 1998) in a complex analytical task that integrates perceived details into an organized structure (McCarthy &Warrington, 1990)” (Lara et al., 2004, p. 386).
Cognitive state of visual perception can be better understood with VOSP in normal and pathological population (Lara et al., 2004). For example, when VOSP was administered to patients of Alzheimer’s disease, impairment was found only in the silhouette subtest of VOSP (Binetti et al., 196 as cited in Lara et al., 2004). This suggests that early perceptual processes are still intact in patients who are in the initial stage of Alzheimer’s disease (Binetti et al., 196 as cited in Lara et al., 2004).
VOSP is clearly a test of object recognition and space perception and nothing else. The is due to the reason , VOSP is made of different tests which includes tasks which are so designed that they assess specific dissociable aspects of object and space perception (Lawrence et al., 2000 , p.1350). Every task of the test focuses on a particular aspect of visual perception being completely independent of other cognitive and motor processes (Lawrence et al., 2000). Hence, VOSP can be regarded as a sensitive test battery.
The authors of VOSP have stated, “Any number of the eight individual tests may be administered and there is no prescribed order (Warrington & James, 1991, p.7)” (Merten, 2006, p.460). This is a very useful thing to do. It is very practically next to impossible to administer the complete set of tests of VOSP as part of neuropsychological assessment because it will be quite a time consuming process (Merten, 2006). Moreover, as advised by Lasogga & Michel (1994 in Merten,2006), easy to use screening measure can be used to test initial visual perception on the suspected group and only those showing visible deficits will be asked to go through the complete assessment (Merten, 2006).
Ecological validity is supported. Good performance reflects healthy people’s functional memory (Ostrosky-Solis et al., as cited in Strauss et al., 2006) and high levels of daily functioning for psychiatric patients (Meyers & Lange, as cited in Strauss et al., 2006). As far as responsiveness of VOSP is concerned, it identifies right cerebral hemisphere problems, as this hemisphere is dominant for visuospatial abilities (Lezak, 1995). It correlates fairly well with other tests like BORB and Visual Organization test (as given by Merten & Beal, 1999) (Merten, 2006).
Scoring of the test is easy. It does not require complex mathematics. Tasks of the tests are simple and easy to do. All the tests are untimed which is advantageous for patients who will be taking the test as most of them will be having deficits in right hemisphere and they won’t have to pressurize themselves to keep up with the time.
Disadvantages of VOSP
Information about the reliability of each of the individual tests in test battery is not provided in the manual (Muller, 1997 as cited in Merten, 2006). Thus the manual needs to be adequately developed incorporating reliability coefficients.
VOSP was standardized on medical samples who were natives of England. This makes the generalization of the normative data very difficult on populations of other nationalities (Bonello et al., 1997) especially USA. Thus overlooking the influence of cultural factors on performance of VOSP (Bonello et al., 1997).
VOSP was not standardized adequately. For instance, the battery is standardized on sample of individuals whose mean verbal IQ is 110 (Bonello et al., 1997), additionally, all the subtests of VOSP were not administered to the sample on which the test was standardized (Bonello et al., 1997). This raises a question towards the standardization of VOSP in its entirety.
The norms for VOSP battery were established on the basis of performance of the two separate samples. 200 of them took 5 tests of VOSP whereas 150 took the remaining of VOSP tests. Such an administration won’t allow us to determine the effect of fatigue and task familiarity (Bonello et al., 1997).
Bonello et al., 1997 has stated that incomplete letters, dot counting and position discrimination show ceiling effects. In the study done by Bonello et al., 1997 all the participants have score more than 96% in the above names three tests. This is in line with the results of sample on which VOSP was originally standardized. They also scored particularly high in these three tests. Surprisingly, validity studies conducted by Warrington & James, 1991 have put forward that VOSP is sensitive to right hemisphere damage despite the ceiling effect shown by VOSP’s subtests (Bonello et al., 1997).
The test battery has been standardized on medical sample without any cognitive problems as control instead of healthy individual (Bonello et al., 1997). This again might have influenced the standardization of the test. Internal consistency of the tests of VOSP has been reported be low, especially for progressive silhouettes, 0.27, incomplete letters, 0.54 and object decision, 0.58. (Merten, 2006; Bonello et al., 1997).
Though VOSP is very appealing to researchers and clinicians because of the nature of specific tasks it employs (Merten, 2006) but it is unable to point out towards the requirements for the rehabilitation of an individual (Lincoln, 1995). The object decision test of VOSP does not only tests visual perception but places demand on attention and decision making as well (Lawrence et al., 2000). This makes difficult to classify the deficits of Huntington’s disease as that of perception only (Lawrence et al., 2000).
The inter item correlation of most of the test items of the constituting tests of VOSP are very less (Merten, 2006). For example, in silhouettes test of object perception item correlation vary between 0.09 to 0.48 with most of them falling somewhere near to 0.20 (Merten, 2006).
Lara et al., 2004 has reported VOSP to be influenced by age, gender and education. Particularly, age has turned out to be a decisive factor for performing perceptual tasks (Albert, 1998; Bonello et al., 1997; Warrington & James, 1991 as cited in Lara et al., 2004). In the study done by Lara et al., 2004 significant differences in results amongst males and females were found in 5 of the 8 subtests.