• homeostatic plasticity
• binocular rivalry
• binocular phase combination
• binocular combination
• plasticity
• monocular deprivation

Neuroplasticity is the ability of brain’s neural networks to change through growth and reorganization. Ocular dominance plasticity (ODP) is commonly the gold standard for studying cortical plasticity, both in humans and in animals. The most utilized method to explore ODP is monocular deprivation (MD), a technique that was firstly used in cats by the neurophysiologists Hubel and Wiesel (1963). They discovered that long-term MD (in the order of weeks) during critical period leads to a permanent shift of ocular dominance in favour of the non-deprived eye with a permanent loss of function of the deprived eye.
Mammalian visual cortex was thought to show little plasticity after closure of the critical period. Nevertheless, it has been recently demonstrated that residual neuroplasticity can be found in human’s adult visual system. In particular, several works have proved that a short-term MD (2-2.5 hours) induces a temporary perceptual shift of ocular dominance: the contribution of the deprived eye to perception is temporary boosted. This result is surprisingly since, contrarily to long-term MD, it induces a strengthening of the deprived eye.

The aim of my thesis is to investigate the residual neuroplasticity in the adult humans visual system by mean of short-term MD. To measure the perceptual ocular dominance two standard methods were used, binocular rivalry and binocular combination. Since the two methods detect different neural mechanisms at the base of ocular dominance, my work aims to compare the results of the two techniques in order to highlight similarities and differences between them. Furthermore the present work aims to investigate whether the shift of ocular dominance is modulated by the duration of deprivation. For this purpose we compare the shift of ocular dominance induced by two distinct deprivation durations.

In concrete terms this work investigate the effect of 120 and 15 minutes MD on ocular dominance measuring it by mean of binocular rivalry and binocular combination. The experiment consist of four experimental conditions: 15 minutes MD tested with binocular rivalry; 15 minutes MD tested with binocular combination; 120 minutes MD tested with binocular rivalry; 120 minutes MD tested with binocular combination. All subjects participate in all the experimental conditions. Each of the four experimental sessions consisted of three stages: a baseline measurement of binocular balance; deprivation stage; five post-patching measurement of binocular balance performed at regular intervals up to 90 minutes after patch removal.

The results reveal a clear effect of duration of deprivation on MD effect captured by both techniques. In particular both techniques registered, in line with previous findings, a strong shift in favour of the deprived eye after 120 minutes of deprivation that persist up to 90 minutes after patch removal, whereas in case of 15 minutes deprivation, both techniques registered a weak shift visible only immediately after patch removal. For both the deprivation duration the peak and recovery highlighted by the two techniques is really similar.
Regarding the difference between techniques, the results reveal that the two ocular dominance measurements strongly correlates in the way they measure ocular dominance, both before and after deprivation. Furthermore, the two techniques correlate in the way they measure the effect of deprivation. These results suggest that the techniques measure similar aspects of ocular balance, hence the two underlying neural mechanisms could be related, and also that short-term MD affects the two mechanisms in a similar fashion.