Approaching objects cause confusion in patients with Alzheimer's disease regarding their direction of self-movement

ArticleinBrain 133(9):2690-701 · September 2010with14 Reads
DOI: 10.1093/brain/awq140 · Source: PubMed
Abstract
Navigation requires real-time heading estimation based-on self-movement cues from optic flow and object motion. We presented a simulated heading discrimination task to young, middle-aged and older adult, normal, control subjects and to patients with mild cognitive impairment or Alzheimer's disease. Age-related decline and neurodegenerative disease effects were evident on a battery of neuropsychological and visual motion psychophysical measures. All subject groups made more accurate heading judgements when using optic flow patterns than when using simulated movement past earth-fixed objects. When both optic flow and congruent object were presented together, heading judgements showed intermediate accuracy. In separate trials, we combined optic flow with non-congruent object motion, simulating an independently moving object. In the case of non-congruent objects, almost all of our subjects shifted their perceived self-movement to heading in the direction of the moving object. However, patients with Alzheimer's disease uniquely indicated that perceived self-movement was straight-ahead, in the direction of visual fixation. The tendency to be confused by objects that appear to move independently in the simulated visual scene corresponded to the difficulty patients with Alzheimer's disease encountered in real-world navigation through the hospital lobby (R(2) = 0.87). This was not the case in older normal controls (R(2) = 0.09). We conclude that perceptual factors limit safe, autonomous navigation in early Alzheimer's disease. In particular, the presence of independently moving objects in naturalistic environments limits the capacity of patients with Alzheimer's disease to judge their heading of self-movement.
    • "Although it is not clear the passage of the signals that activated MST responses in the Huk et al. (2002) study, perhaps, the same signals may account for the performance observed in the central vision condition of the present study as well as that of the Kim (2013) study. Duffy and colleagues ( Duffy, 1999, 2003; Tetewsky and Duffy, 1999; O'Brien et al., 2001; Kavcic and Duffy, 2003; Mapstone et al., 2003 Mapstone et al., , 2008 Monacelli et al., 2003; Duffy et al., 2004; Kavcic et al., 2006; Mapstone and Duffy, 2010) demonstrated that the inability to extract heading information from radial optic flow contributes to AD patients' difficulties in navigation and visuospatial orientation. Additional impairment in extracting ˙ τ from looming optical patterns would exacerbate AD patients' navigational difficulties. "
    [Show abstract] [Hide abstract] ABSTRACT: The present study explored whether the optic flow deficit in Alzheimer’s disease (AD) reported in the literature transfers to different types of optic flow, in particular, one that specifies collision impacts with upcoming surfaces, with a special focus on the effect of retinal eccentricity. Displays simulated observer movement over a ground plane toward obstacles lying in the observer’s path. Optical expansion was modulated by varying τ˙. The visual field was masked either centrally (peripheral vision) or peripherally (central vision) using masks ranging from 10° to 30° in diameter in steps of 10°. Participants were asked to indicate whether their approach would result in “collision” or “no collision” with the obstacles. Results showed that AD patients’ sensitivity to τ˙ was severely compromised, not only for central vision but also for peripheral vision, compared to age- and education-matched elderly controls. The results demonstrated that AD patients’ optic flow deficit is not limited to radial optic flow but includes also the optical pattern engendered by τ˙. Further deterioration in the capacity to extract τ˙ to determine potential collisions in conjunction with the inability to extract heading information from radial optic flow would exacerbate AD patients’ difficulties in navigation and visuospatial orientation.
    Full-text · Article · Nov 2015
    • "In monkey single neurons, we found competitive attentional control between pattern and object motion [24]. In human studies, we found that this competition uniquely disrupts perception in early AD [25]. Such attentional control of sensory processing has been seen in ERP amplitudes [26,27], evoked power [28,29,30] , and phase coher- ence [31,32]. "
    [Show abstract] [Hide abstract] ABSTRACT: Our goal is to understand the neural basis of functional impairment in aging and Alzheimer's disease (AD) to be able to characterize clinically significant decline and assess therapeutic efficacy. We used frequency-tagged ERPs to word and motion stimuli to study the effects of stimulus conditions and selective attention. ERPs to word or motion increase when a task-irrelevant 2nd stimulus is added, but decrease when the task is moved to that 2nd stimulus. Spectral analyses show task effects on response power without 2nd stimulus effects. However, phase coherence shows both 2nd stimulus and task effects. Thus, power and coherence are dissociably modulated by stimulus and task effects. Task-dependent phase coherence successively declines in aging and AD. In contrast, task-dependent spectral power increases in aging, only to decrease in AD. We hypothesize that age-related declines in signal coherence, associated with increased power generation, stresses neurons and contributes to the loss of response power and the development of functional impairment in AD.
    Full-text · Article · Sep 2014
    • "The most extensively studied central visual function in AD is motion processing, in particular as determined by radial optic flow. Psychophysical analysis has revealed that AD patients exhibit exquisite deficits in differentiating movement directions inferred from optic flow195196197. Further neurophysiological studies suggest that both the sensory/perceptual components and the cognitive components involved in motion perception under optic flow are affected in early AD patients as both the earlier and later components of ERP signals are diminished under a variety of experimental paradigms198199200201. "
    [Show abstract] [Hide abstract] ABSTRACT: Recent evidence indicates that sensory and motor changes may precede the cognitive symptoms of Alzheimer's disease (AD) by several years and may signify increased risk of developing AD. Traditionally, sensory and motor dysfunctions in aging and AD have been studied separately. To ascertain the evidence supporting the relationship between age-related changes in sensory and motor systems and the development of AD and to facilitate communication between several disciplines, the National Institute on Aging held an exploratory workshop titled “Sensory and Motor Dysfunctions in Aging and AD.” The scientific sessions of the workshop focused on age-related and neuropathologic changes in the olfactory, visual, auditory, and motor systems, followed by extensive discussion and hypothesis generation related to the possible links among sensory, cognitive, and motor domains in aging and AD. Based on the data presented and discussed at this workshop, it is clear that sensory and motor regions of the central nervous system are affected by AD pathology and that interventions targeting amelioration of sensory-motor deficits in AD may enhance patient function as AD progresses.
    Full-text · Article · Jul 2014
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