In the following sections, English summaries of the three studies presented in this dissertation are given. For a detailed German synopsis of the present work, see chapter 8 (pp. 118 et seqq.).
Research in the field of aging and dementia is a main concern as the population of elderly people is growing continuously due to increasing life expectancy and thus, an accumulative number of people who live well beyond 65 years of age run a risk of developing age-associated neurodegenerative disorders of cognitive function, such as Alzheimer’s disease (AD), emerging as a major health problem.
The present work is based on growing evidence that deficits in visual selective attention occur early in the progression to AD (Foldi et al., 2002) and therefore might be present as the first non-memory deficits (Perry & Hodges, 1999) at the early prodromal stage of mild cognitive impairment (MCI; Petersen et al., 1999). The present dissertation was performed to contribute to the still ongoing debate as to whether certain aspects of visual selective attention are par-ticularly vulnerable or preserved, especially at the stage of MCI, and whether attentional func-tioning might be qualitatively and/ or quantitatively different from attentional performance at the AD stage on the one hand or normal functioning on the other hand.
As theoretical basis, Bundesen’s theory of visual attention (TVA; Bundesen, 1990, 1998) was employed to assess several latent, mathematically independent and quantitative parameter es-timates which are derived from two highly comparable paradigms – computerized whole re-port and partial report of briefly presented visual letter arrays. Central conclusions arising out of TVA-based investigations (e.g., Bublak et al., 2005; Bublak, Redel, & Finke, 2006; Duncan et al., 1999; Duncan et al., 2003; Finke et al., 2006; Gerlach, Marstrand, Habekost, & Gade, 2005; Habekost & Bundesen, 2003; Habekost & Rostrup, 2006; Peers et al., 2005) point at four central strengths of this tool for attentional assessment – the quality criteria sensitivity, specificity, reliability and validity.
Study 1:
In AD, the amyloid cascade hypothesis (Hardy & Selkoe, 2002) assumes that rising plaque and tangle burden invokes loss of nerve cells through direct and indirect effects on synaptic, neuronal and neuritic function (see e.g. Cirrito et al., 2005), resulting in progressive intellectual decline. Thus, sensitive biomarkers loading functionally on the neural alterations invoked by AD from early on, might improve the possibility to identify at risk subjects in time, providing a chance for effective treatment (Shah et al., 2008). The first study (see chapter 4, pp. 31 et seqq.) examined whether cognitive parameters for estimating the capacity of visual attention might serve that purpose.
Based on Bundesen’s (1990) TVA, visual information uptake was analyzed in 18 subjects with probable AD, 18 subjects with amnestic MCI, and 18 healthy elderly control subjects. Groups were matched for gender, age, and education. From a whole report task requiring ver-bal report of briefly presented letters, four parameters were derived, characterizing different aspects of visual processing capacity: perceptual threshold t0, iconic memory μ, processing speed C, and visual short-term memory (VSTM) storage capacity K.
Comparison of these attentional parameters between groups revealed an elevation of the per-ceptual threshold already in MCI subjects, while processing speed and VSTM storage capacity showed a significant decline for AD patients, only. AD patients on medication with acetyl-choline esterase inhibitors had higher processing speed, but were still below the level of MCI patients. Perceptual threshold values were significantly correlated with disease duration, but not with cognitive measures. Conversely, speed and VSTM were significantly related to cog-nitive scores, but not to disease duration. In particular, VSTM storage was related to neurop-sychological tasks applyi