Independent Deficits of Visual Word and Motion Processing in Aging and Early Alzheimer's Disease

Abstract

We tested whether visual processing impairments in aging and Alzheimer's disease (AD) reflect uniform posterior cortical decline, or independent disorders of visual processing for reading and navigation. Young and older normal controls were compared to early AD patients using psychophysical measures of visual word and motion processing. We find elevated perceptual thresholds for letters and word discrimination from young normal controls, to older normal controls, to early AD patients. Across subject groups, visual motion processing showed a similar pattern of increasing thresholds, with the greatest impact on radial pattern motion perception. Combined analyses show that letter, word, and motion processing impairments are independent of each other. Aging and AD may be accompanied by independent impairments of visual processing for reading and navigation. This suggests separate underlying disorders and highlights the need for comprehensive evaluations to detect early deficits.

Ocular and Visual Manifestation of Alzheimer’s Disease: A Literature Review II Part: Clinical Studies

“…Several authors examined visual deficits using neuropsychological tests and reaching discordant results. Indeed some recognized visuospatial deficits in the early stages (5,29) whereas others found evidence only in the latter stages of the disease (30,31). According to Paxton et al (30), these deficits may be useful in tracking the disease's course.…”

“…According to Paxton et al (30), these deficits may be useful in tracking the disease's course. Some authors identified a selective damage of the posterior pathway (32) whereas others claimed that AD affects multiple visual pathways and regions (29). The ocular motility is controlled by a complex network (33), which can easily be damaged by pathological processes and has therefore been extensively examined in AD research.…”

Motion‐induced position mis‐localization predicts the severity of Alzheimer's disease

“…Previous studies have shown that AD patients were associated with abnormal gait speed during walking (Buracchio, Dodge, Howieson, Wasserman, & Kaye, ; Verghese, Wang, Lipton, Holtzer, & Xue, ), impaired olfactory processing (Devanand et al ., ; Mesholam, Moberg, Mahr, & Doty, ; Murphy, Gilmore, Seery, Salmon, & Lasker, ), auditory deficits (Gallacher et al ., ; Lin et al ., ), and the loss of visual perceptual functions (Cronin‐Golomb, Corkin, & Growdon, ; Rizzo & Nawrot, ; Tetewsky & Duffy, ). In the vision domain, perceptual impairments have so far been reported in the form of colour discrimination (Pache et al ., ; Wijk, Berg, Sivik, & Steen, ), letter/word discrimination (Velarde, Perelstein, Ressmann, & Duffy, ), contrast sensitivity (Cronin‐Golomb et al ., ), and in particular, visual motion sensitivity (Gilmore et al ., ; Kavcic et al ., ; Mapstone et al ., ). Several of these perceptual dysfunctions are predictive of progression towards AD (Cronin‐Golomb et al ., ; Devanand et al ., , ), thus holding potential promise for non‐invasive early detection of AD and/or the tracking of disease development.…”

Repetition priming and cortical arousal in healthy aging and Alzheimer's disease

“…First, posterior perceptual systems have been found to be disrupted in AD (e.g., Festa, Insler, Salmon, Paxton, Hamilton & Heindel, 2005; Hof & Morrison, 1990; Paxton et al, 2007; Velarde, Perelstein, Ressmann & Duffy, 2012) and perceptual repetition priming is not entirely intact (e.g., Backman, Almkvist, Nyberg & Andersson, 2000; Bondi & Kaszniak, 1991; Heindel, Salmon & Butters, 1990; Heindel, Salmon, Fennema-Notestine & Chan, 1998). Second, meta-analyses of word-stem completion priming studies in AD have confirmed the overall presence of a significant priming deficit (Meiran & Jelicic, 1995; Millet et al, 2010), but have also noted considerable variability in the magnitude of the deficit.…”