Visual-motor embodiment of language: a few implications for the neuropsychological evaluation (in Alzheimer's disease).

Abstract

For several decades, researchers in cognitive neuroscience and cognitive psychology have developed works concerning the close relationships between “lower-level” perceptual/motor and “higher-level” conceptual/linguistic processes (Harnad, 1987; Goldstone, 1994; Barsalou, 1999; Pulvermuller and Fadiga, 2010). Some of them suggested to “reunit” perception and conception (Goldstone and Barsalou, 1998), studied the interactions between language and action (Glenberg and Kaschak, 2002; see Pulvermuller and Fadiga, 2010, for a global picture in neuroscience), or were interested in the relationships between language and other bodily (emotional) states (Glenberg et al., 2005). On the neurophysiological and ophthalmological grounds, contemporary studies suggest that not only does Alzheimer's Disease (AD) lead to alteration in brain cortical structure and cognitive impairment, but it also conducts to deep changes in both visual system organization and vision-based performances (Tzekov and Mullan, 2013). We recommend that both the perceptual impairment found in AD and the interactions between lower-level and higher-level cognition be taken into account by neurospychologists in order to avoid misattribution of performance deficits. We first mention a recent research concerning language evaluation in AD and discuss main limitations of modular evaluation in that type of context. Then, we present main features of the visual “function” impairment in AD, the impacts of perceptual changes over higher-level cognition, and finally, we provide general recommendations for neuropsychological testing of higher-level cognitive “functions”. Linguistic evaluation in AD Drummond et al. (2015) reported an interesting research in which language production processes were evaluated in patients with AD, amnestic mild cognitive impairment (a-MCI), and controls. In contrast with many neuropsychological tests aiming at evaluating language on the basis of simple concept production (e.g., naming), the authors developed a “narrative test,” in which participants were supposed to narrate a story from a sequence of visually presented actions. Overall, the authors found that patients with a-MCI already presented narrative deficits in comparison with the control group. Interestingly, a-MCI discursive deficits were lower than those presented by patients with AD, which may be interpreted as an intermediate level of deficiency between healthy elderly and patients with AD. The research is interesting and allows us to examine usual practices in neuropsychology and neuropsychological research. Although the participants in this kind of research generally undergo both neuropsychological and visual (i.e., acuity) assessments, the real involvement of language “function” in the deficits found in patients with AD or a-MCI can be questioned. As we will see later, AD can lead to several visual processing impairments that influence higher-level cognitive performance so that checking for normal or corrected-to-normal visual acuity is not sufficient to control for lower-level influence on cognitive performance. Typically, whether in neuropsychology or in speech therapy, language abilities in AD are often evaluated by tests involving the visual “function”. For instance, in the naming tests, patients have to orally produce the word represented by a drawing picture. Similarly, oral comprehension tests ask patients to indicate, among several pictures, which corresponds to a word or a sentence read by the examiner. In other words, patients have to visually recognize a picture (as in the naming tests) based on an oral description. The matching category tests also require patients to choose—among several visual items—the one that is semantically associated with a target item. Finally, tests that focus on graphic abilities (e.g., dictation, free writing, writing description) also rely on visual “functions”. When performances are altered in the tests such as those described above, any earlier level of information processing can be involved (Greene, 2005). Although they are mainly employed to evaluate language, these tests can also reflect visual “function” impairment. The semantic recognition of drawings or pictures implies that patients rely on good visual acuity, color vision, contrast sensitivity, and oculomotor processing. Misinterpretations of AD patient troubles may arise if visual performances are not taken into account (and controlled for in statistical analyses).