Eye vergence responses to novel and familiar stimuli in young children

Altered Vergence Eye Movements and Pupil Response of Patients with Alzheimer's Disease and Mild Cognitive Impairment During an Oddball Task

BACKGROUND

Alzheimer's disease (AD) is characterized by progressive deterioration of cognitive functions and may be preceded by mild cognitive impairment (MCI). Evidence shows changes in pupil and vergence responses related to cognitive processing of visual information.

OBJECTIVE

Here we test the hypothesis that MCI and AD are associated with specific patterns in vergence and pupil responses.

METHODS

We employed a visual oddball task. In the distractor condition (80%of the trials), a blue stimulus was presented whereas in the target condition (20%of trials) it was red. Participants (23 Controls, 33 MCI patients, and 18 AD patients) were instructed to press a button when a target appeared.

RESULTS

Participants briefly converged their eyes 200 ms after stimulus presentation. In controls, this transient peak response was followed by a delay response to targets but not to distractor stimuli. In the patient groups, delay responses to distractors were noticed. Consequently, the differential vergence response was strong in the control group, weak in the MCI group, and absent in the AD group. Pupils started to dilate 500-600 ms after the appearance of a target but slightly contracted after the presentation of a distractor. This differential pupil response was strongest in the AD group.

CONCLUSION

Our findings support the idea of a role of vergence and pupil responses in attention and reveal altered responses in MCI and AD patients. Further studies should assess the value of vergence and pupil measurements as an objective support tool for early diagnosis of AD.

Vergence eye movements during figure-ground perception

Figure-ground, that is the segmentation of visual information into objects and their surrounding backgrounds, provides structure for visual attention. Recent evidence shows a novel role of vergence eye movements in visual attention. In the present work, vergence responses during figure-ground segregation tasks are psychophysically investigated. We show that during a figure-ground detection task, subjects convergence their eyes. Vergence eye movements are larger in figure trials than in ground trials. In detected figures trials, vergence are stronger than in trials where the figure went unnoticed. Moreover in figure trials, vergence responses are stronger to low-contrast figures than to high-contrast figures. We argue that these discriminative vergence responses have a role in figure-ground.

Eye vergence responses in children with and without reading difficulties during a word detection task

Vergence eye movements are movements of both eyes in opposite directions. Vergence is known to have a role in binocular vision. However recent studies link vergence eye movements also to attention and attention disorders. As attention may be involved in dyslexia, it is sensible to guess that the presence of reading difficulties can be associated with specific patterns in vergence responses. Data from school children performing a word-reading task have been analysed. In the task, children had to distinguish words from non-words (scrambled words or row of X's), while their eye positions were recorded. Our findings show that after stimulus presentation eyes briefly converge. These vergence responses depend on the stimulus type and age of the child, and are different for children with reading difficulties. Our findings support the idea of a role of attention in word reading and offer an explanation of altered attention in dyslexia.