Recent psychophysical and neuroimaging studies provide a computational description of how object recognition is achieved from low-level features detection, through mid-level integration, to high-level object category representation. These discoveries provide essential tools to address the acquired object recognition deficits in patients.
In this project we design a set of tasks based on what is known from the psychophysical literature to evaluate the perceptual chain from low- to high-level processing. Based on previous studies of this research group a series of experiments are designed to address: visual field, visual acuity, saccade execution and exploratory eye-movements, feature integration, visual span, contextual effects and visuo-spatial attention.
These tasks enable to evaluate the interaction between task demand, impaired visual field and perceptual integration processes in patients. The preliminary data obtained will have important implications for designing a new screening battery to assess visual disabilities. We foresee that the results will prove useful in defining ad-hoc rehabilitation protocols for stroke and posterior cortical atrophy patients, taking into account the specific functions involved in the task.
Recent psychophysical models provide a valuable insight into objects recognition that enable the assessment of the patients' visual deficits. Integration is a key concept enabling to overcome the ill defined ideas of perceptual grouping derived from Gestalt psychology that still guide the design of assessment batteries (e.g., see The Leuven Perceptual Organization Screening Test 2015
Here we defined a perceptually hierarchical assessment procedure able to evaluate the knocked out functions in the object recognition hierarchy.
The category selectivity of the patients' impairments reported in the literature is still largely a mystery. A line of research on posterior cortical atrophy (PCA) has suggested that patients with impairments across a range of visual tasks may have intact reading, and it has been argued that this contradicts the hypothesis that a general visual deficit is the cause of category selective loss in recognition, such as pure alexia, (e.g., Yong et al. 2013; 2016). In addition, it has been demonstrated that as the PCA progresses, there is a concurrent development of deficits in crowding and reading in these patients (Yong et al., 2016). Parallely it has been argued that selective deficits are likely to be caused by a general visual deficit, although in pure alexia one that has a disproportionate effect on reading compared to other visual tasks (e.g., Starrfelt et al., 2009; Starrfelt & Behrmann, 2011), as well as a disproportionate effect on foveal compared to peripheral vision (Starrfelt et al., 2010). Current findings suggest that the reading deficit maybe due to an impaired transmission of the perceptual representation to the word units, rather than to an abnormal integration of the object parts, i.e. letters in words. However, it seems that prosopagnosic and pure alexic patients dissociate on a comparatively low level measure of vision, the crowding measure (Sand et al., 2018).
Here we conjecture that an interaction between task demand, impaired visual field and perceptual integration processes may be at the route of the observed discrepancies.
In particular the experimental set will provide information relative to the role of the visual field, eye-movements, perceptual and attentional impairments in determining the behavioral difficulties with visual objects.
This preliminary research proposal will have two important implications. Designing a screening battery based on what is known about psychophysical computational models and defining ad-hoc rehabilitation protocols that take into account the specific compromized functions involved in the task.