Visual search patterns in semantic dementia show paradoxical facilitation of binding processes

Abstract

While patients with Alzheimer’s disease (AD) show deficits in attention, manifested by inefficient performance on visual search, new visual talents can emerge in patients with frontotemporal lobar degeneration (FTLD), suggesting that, at least in some of the patients, visual attention is spared, if not enhanced. To investigate the underlying mechanisms for visual talent in FTLD (behavioral variant FTD [bvFTD] and semantic dementia [SD]) patients, we measured performance on a visual search paradigm that includes both feature and conjunction search, while simultaneously monitoring saccadic eye movements. AD patients were impaired relative to healthy controls (NC) and FTLD patients on both feature and conjunction search. BvFTD patients showed less accurate performance only on the conjunction search task, but slower response times than NC on all three tasks. In contrast, SD patients were as accurate as controls and had faster response times when faced with the largest number of distracters in the conjunction search task. Measurement of saccades during visual search showed that AD patients explored more of the image, whereas SD patients explored less of the image before making a decision as to whether the target was present. Performance on the conjunction search task positively correlated with gray matter volume in the superior parietal lobe, precuneus, middle frontal gyrus and superior temporal gyrus. These data suggest that despite the presence of extensive temporal lobe degeneration, visual talent in SD may be facilitated by more efficient visual search under distracting conditions due to enhanced function in the dorsal frontoparietal attention network.

Characterisation of “Positive” Behaviours in Primary Progressive Aphasias

“…Novel or increased activities were found in all categories in the svPPA group, with the most common being an interest in puzzle activities (32%), which is in line with previous reports [18,34]. On the other hand, differences in the prevalence of artistic activities emerged between the nonfluent PPA subtypes.…”

What do we Know About Eye Movements in Alzheimer’s Disease? The Past 37 Years and Future Directions

“…Consistently an fMRI study evidenced reduction in right intraparietal sulcus activation suggesting that left-dominant laterality ratio for intraparietal sulcus may be a marker of AD progression [12]. The study of selective attention has revealed an excess of saccades, fixation and pupil dilation in visual search and feature-and-conjunction search, which is interpreted as dynamic adjustment of attentional zoom or loss of access to attentional resources, consistent with compensatory over recruitment of frontoparietal attention network [13]. An important set of literature (12.1%) was devoted to one attentional control process -inhibition.…”

Eye Movements in Alzheimer's Disease

“…Consistent with this interpretation, patients exhibit greater pupil dilation during difficult searches that are defined by a conjunction of target feature values, suggesting that they expend more attentional resources on searches that place greater demand on visual processing [89]. Notably, patients are able to find search targets at a comparable rate to controls, yet they still have longer response times [92]. The extended response times in patients most likely reflect slower target processing in AD, although longer motor responses may also play a minor role [90].…”

“…Compared to healthy controls, patients are less accurate and have longer response times in visual search tasks [89-92]. Patients’ eye movement patterns during search have been characterized as disorganized and stochastic [31,90].…”

“…Additionally, the duration of fixations while searching is notably longer in AD [31,90,91]. Declines in visual search behavior in AD patients have been associated with decreased gray matter in bilateral parietal lobes, precuneus, occipital, temporal, and frontal lobes [92]. …”