What does the object decision task measure? Reflections on the basis of evidence from semantic dementia.

Abstract

The authors investigated the impact of semantic knowledge on visual object analysis by assessing the performance of patients with semantic dementia on a different-views object matching test and on 2 object decision tests differing, for example, in whether the nonreal items were nonsense objects or chimeras of 2 real objects. On average, the patients scored normally on both the object matching and the object decision test including nonsense objects but were impaired on the object decision test including chimeras; this latter was also the only visual object test that correlated significantly with degree of semantic impairment. These findings demonstrate that object decision is not a single task or ability and that it is not necessarily independent of conceptual knowledge.

Specialization in the medial temporal lobe for processing of objects and scenes

“…One possible explanation for this finding is that semantic knowledge about the highly familiar objects (of which existing perceptual representations may be a critical component) facilitated performance on the familiar object task, leading to faster response times and significantly improved task accuracy. In support of this, there have been recent reports that semantic knowledge can influence performance on visual processing tasks, for example, by aiding the perception of object silhouettes (Hovius et al, 2003) or impeding performance on a visual search task if the target and distractor items are semantically associated (Moores et al, 2003).…”

The anatomy of semantic knowledge: Medial vs. lateral temporal lobe

“…CON-1 for these 7 tests refers to 9 controls (6 female, mean age ϭ 61 years, education ϭ 11 years), also from Hodges et al (15). The data for the 11 patients (7 male) who took the Object Decision test were reported by Hovius et al (16). The patients averaged 63.3 years of age (range ϭ 52-78 years) and 11.6 years of education, and their 21 controls (CON-4) averaged 68.5 years of age and 11.0 years of education.…”

“…In the Object͞ Nonobject Discrimination Task (27,28), participants saw line drawings of real objects and chimeric nonobjects (created by cutting and pasting parts of real objects) and were asked to indicate whether the object was real or not. The data reported for patients with SD and their controls (16) are from a test consisting of 32 real and 32 chimeric objects. The data for amnesic patients and their controls are from a similar test consisting of 30 items of each type.…”

“…Much of the data for the MTL group has been published (5). The data for SD come from a series of related publications that describe the pattern of sparing and loss in SD (15)(16)(17)(18).…”

"Presemantic" Cognition in Semantic Dementia: Six Deficits in Search of an Explanation

“…On the other hand, where this has been evaluated, patients with SD are typically impaired on some cognitive processes that are usually thought to be performed largely without reference to or need for conceptual knowledge: the ''presemantic'' cognition in the title of this article. Six examples of such impairments in SD are: reading aloud single written words (Fushimi et al, 2003;Funnell, 1996;; spelling single spoken words (Graham, Patterson, & Hodges, 2000;Parkin, 1993); transforming the stem (present tense) forms of verbs into their corresponding past-tense forms (Patterson, Lambon Ralph, Hodges, & McClelland, 2001;Cortese, Balota, Sergent-Marshall, Buckner, & Gold, in press); judging whether orthographically well-formed letter strings represent real words, that is, lexical decision Moss, Tyler, Hodges, & Patterson, 1995;Diesfeldt, 1992); judging whether line drawings of possible objects represent objects that really exist, that is, object decision (Hovius, Kellenbach, Graham, Hodges, & Patterson, 2003;Breedin, Saffran, & Coslett, 1994); and reproducing simple line drawings of familiar objects after a short (e.g., 10 sec) delay (Bozeat et al, 2003;Lambon Ralph & Howard, 2000).…”