David Dulin

Effects of peripheral and central visual impairment on mental imagery capacity

This paper reviews a number of behavioral, neuropsychological and neuroimaging studies that bear on the question of whether and how visual disorders of peripheral or central origin lead to disorders of mental imagery capacity. The review of the literature suggests that in cases of blindness of peripheral origin lack of vision can progressively lead to representational disorders. However, in patients suffering from peripheral visual deficits, representational disorders can partially or completely be compensated by other sensory modalities as well as by cortical reorganization. Interestingly, in brain-damaged patients, neurovisual disorders following occipital or parietal lesions are not systematically associated with representational deficits, thus demonstrating that visual perception and visual imagery may not rely on the same cortical structures as previously hypothesized. Impairments seen on mental imagery tasks among brain-damaged patients with visual and/or spatial deficits might be due to an often co-existing attentional deficit. We discuss this possible dissociation between visual perception and visual mental imagery and its implications for theoretical models of mental representation.

Colour, face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental imagery disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional–exploratory mechanisms that are employed in visual behaviour.

Effects of Central Vision, Peripheral Vision, and Haptic Inputs on Complex Verbal and Spatial Tasks

The aim of the present study is to investigate how quite specific sensory inputs (visual inputs from central or peripheral regions of the retina and haptic inputs) relate to complex cognitive performance. We compare individuals with severe peripheral visual field loss, Braille reader with central scotomata (SDB group), print readers with central scotomata, and normally sighted people on visual reading and spatial imagery tasks. Experiment 1 showed that the SDB subjects were significantly less accurate than the other groups on reading visual print letters, words, digits, and 4-digit numbers aloud. In experiment 2, SDB subjects also performed worse than the other subjects on imagery tasks that required indicating spatial characteristics of orally presented print letters, rotated capital letters, print words, and number shapes. Experiment 3 revealed that the SDB group improved their performance when instructed to draw the outlines of imagined stimuli shapes haptically. The findings suggest that visual memory needs perceptual practice to be maintained and that haptic inputs can be used to improve verbal and spatial imagery skills in visually impaired individuals.

Accurate High Throughput Bright Field Bead Tracking using Gpu Hardware

With the recent advances in camera technology, the potential of microscopy to study the behaviour of single molecules can make great strides. Here, we present a highly-optimized method to track magnetic beads in a bright-field microscopy setup that takes full advantage of both new camera technology and fast graphics hardware to do parallel computations. Using large field-of-view cameras, we can carry out real-time tracking of hundreds of magnetic beads in parallel while maintaining nanometer-scale accuracy. Additionally, we can use fast CMOS cameras to perform real-time bead tracking at an acquisition rate of several kHz. These advances allow us to use the magnetic tweezer as a tool to acquire detailed statistical knowledge at high temporal resolution of the behaviour of single molecules or molecular complexes.

Haptic Learning of Spatial Concepts: Can Training in Raised-Line Drawings Improve Blind People's Spatial Capacity?

The purpose of this research was to evaluate the impact of instruction in raised-line drawings on the spatial imagery capacity of congenitally and late blind people. The participants first performed preliminary tasks in order to evaluate their individual level of experience in the recognition and production of raised-line drawings. Then, all the participants (experienced congenitally and late blind groups, non-experienced congenitally and late blind groups, and blindfolded sighted participants) were presented with a mental rotation task, a mental spatial displacement task, and a direction judgment task. After this pre-test, half of the non-experienced participants (congenitally and late blind) were trained for 6 months in the recognition and production of raised-line drawings. Then, all the groups were presented again with the 3 spatial tasks (post-test). Results showed that the experienced participants performed better than the non-experienced ones in all the spatial imagery tasks of the pre-test. Contrary to the non-trained participants, the trained participants improved their skills as revealed during the post-test, and they performed as well as the non-trained experienced blind groups on all the spatial tasks of the post-test. These data indicate that a short yet intensive training of the blind people had a significant effect and that the benefits generalize to other spatial tasks (i.e., mental rotation, mental spatial displacement, and direction judgment tasks). In addition to a better understanding of blind peoples cognitive functioning, these results may have important implications regarding the value of line drawing training in the education of visually impaired people.