The primary goal of our study was to assess the independent contribution of executive functioning and language skills to HVOT performance among cognitively intact geriatric participants and individuals with MCI. Our hypotheses were partially supported, as one element of executive functioning (i.e., rapid word generation as assessed by COWA) accounted for the most variance among the NC group. Additionally, age and naming ability were modestly associated with HVOT performance. Collectively, these findings suggest that HVOT performance among geriatric controls is more strongly related to executive functioning; however, to a lesser extent, advanced age and language are associated with task completion. These data compliment the extant literature, as Libon et al. (1994)
found that integrative visuospatial tasks, defined as those requiring substantial integrational ability, were strongly correlated with executive function tests, including COWA. Furthermore, neuroimaging evidence among normal controls suggests HVOT performance is associated with bilateral activation that includes not only parietal and occipital areas but also the lateral inferior/middle precentral gyrus within the left frontal lobe (Moritz, Johnson, McMillan, Haughton, & Meyerand, 2004
). Thus, our findings are consistent with previous reports of an association between HVOT performance and executive functioning or frontal regions mediating such cognitive tasks.
Among the MCI sample, our hypotheses were again partially supported. HVOT performance was associated with lexical retrieval ability; however, executive functioning measures were not significant predictors. There are a couple of possible explanations for this finding. First, the unexpected association of naming with HVOT performance among the MCI participants may be related to the fact that MCI often reflects prodromal AD (Petersen et al., 1999
). It is well known that AD involves progressive deterioration of multiple cognitive systems, of which naming is often a prominent symptom. Therefore, many MCI participants in our sample likely have mild naming difficulties consistent with preclinical AD, which could account for the association between the BNT and HVOT. It is noteworthy to mention that among the non-amnestic single-domain MCI participants (n
= 32), BNT performance was not utilized in determining language impairment. Rather, alternate language tasks included in the broader ADCC neurodiagnostic workup were responsible for characterizing subgroup membership for those MCI participants with isolated language impairments. Therefore, we submit that the association between BNT and HVOT performance is not statistically driven by the MCI subtype with isolated language deficits restricted to BNT performance. A second explanation for the unique association between BNT and HVOT is task similarity, as both tests include line drawings of common objects that examinees must name. The tasks’ shared perceptual features appear to be a logical explanation for our findings; however, this explanation is undermined by the absence of a strong association between HVOT and BNT performance in the elderly control sample. Therefore, we propose that naming ability is uniquely associated with HVOT performance among individuals with MCI.
As a secondary aim, the present study compared HVOT performance across several diagnostic categories, including NC, MCI, and AD participants. Consistent with expectation, the NC group outperformed the MCI and AD groups, while the MCI group outperformed the AD group. These findings are the first to report HVOT performances among MCI participants in comparison to other diagnostic categories, and our data support the notion that MCI is often a transitional stage between normal cognitive function and clinically probable AD (Winblad et al., 2004
A strength of our study is the examination of MCI participants, as no study has previously reported HVOT performance among this diagnostic group. Furthermore, we extend previous research (e.g., Libon et al., 1994
; Paul et al., 2001
) by simultaneously examining the impact of executive functioning and language on HVOT performance. Despite these strengths, a few limitations must be considered, which restrict the generalizability of our findings. Though we simultaneously considered the impact of executive functioning and language on HVOT performance, we did not include a visuoperceptual measure to isolate the perceptual demands of the HVOT, as this was not a goal of our study. In the absence of a visuoperceptual covariate, we are unable to specify the extent to which language and or executive function impact HVOT performance above and beyond
visuoperceptual skills. Future investigators may want to simultaneously compare perceptual, linguistic, and executive functioning demands to further elucidate the multifactorial nature of HVOT performance among older adults with and without cognitive impairment.
In summary, this study characterized HVOT performance for MCI participants and identified language and executive functioning correlates of HVOT performance among healthy elders and individuals with MCI. Results suggest NC participants outperform both MCI and AD participants, while MCI participants outperform AD participants. Additionally, rapid word generation, a measure of executive functioning, is the most salient correlate of HVOT performance among NC participants. In contrast, among MCI participants, lexical retrieval is the most salient language or executive functioning correlate of HVOT performance. Taken together, these findings support the notion that MCI is often a transitional stage between normal aging and dementia, and variations in cognitive functions associated with the cognitive aging spectrum account for unique correlates of HVOT performance. Such information is useful in clinical practice when interpreting HVOT performance among older patients suspected of having MCI.