Eye muscle proprioceptive manipulation confirms spatial bias in visual attention towards the perceived direction of gaze
Daniela Balslev, William Newman, Paul C. Knox
My talk is scheduled on Thursday sept 1 at 15:30.
Our conclusion is that attention is involuntarily captured in the perceived direction of gaze. By using passive eye movement, this study provides more direct evidence of the role of eye proprioception in the allocation of attention, than my previous study where we interfered with the cortical processing of eye proprioception using repetitive transcranial magnetic stimulation (rTMS) over the somatosensory cortex.
The experiment was carried out at the University of Liverpool in collaboration with Drs. Knox and Newman. We used a scleral lens to manipulate the eye muscles and measured the consequences of this proprioceptive stimulus on visual accuracy. This proceedure was invented by Gabriel Gauthier and is considered "the golden standard" for testing the effects of eye proprioception on behavior in humans. I was very lucky to work with Paul Knox who is one of the few experts worldwide in using this method, and with William Newman, an ophthalmology consultant who kindly offered a chunk of his very busy time to make sure that the eyes of the experiment participants stayed safe.
The scleral lens is very similar with a hard contact lens that is used in patients. The lens is modified by attaching a tube - through which light suction is created to fix the lens to the cornea - and a stalk - which is fixed in a static holder. First the participant fixates laterally at 10 degrees, allowing us to block the dominant eye in this position. Then s/he is instructed to fixate centrally, causing the non-dominant, viewing eye to rotate back, whereas the non-viewing eye remains deviated. Although this eye returns centrally, its position is perceived to be slightly (~2 degrees) rotated in the direction of the dominant eye. This dissociates the real direction of gaze from the perceived direction of gaze and allows us to test visual detection for targets that are retinotopically equidistant, but presented at different distances from the perceived direction of gaze.
The procedure is not painful, only unpleasant - like putting contact lenses in and out of the eyes...
The abstract of my talk is here.
See you in Toulouse maybe...