File under: “it turns out it’s more complicated than that.”  Many deaf people have better-than-average vision and many studies have shown that the parts of the brain that would be used for hearing are helping out with vision instead. New work from a joint team from universities in Italy and France demonstrates that things may not be as straightforward as we might think. Deaf people may have much better peripheral vision than their hearing counterparts.

In a elegantly simple experiment the team took ten people who had been profoundly deaf since infancy, and ten hearing matched controls, and asked them to carry out a simple target-spotting task (See Figure 1). The participants pressed a key when they saw a target appear in one of eight locations: four close to the centre of the participants’ visual field and four further out in the periphery.

Experimental protocol and behavioural results.

Experimental protocol and behavioural results from Bottari et al (2011).Not only did the participants who had been deaf since childhood respond faster, they also weren't as affected by the position of the stimulus as the participants with unimpeded hearing.The dotted circles in Part a show the eight target locations. The "C" and "Reverse C" shapes are the targets that the participants had to identify.

The researchers discovered that the participants who had been deaf since childhood spotted and responded to the targets much faster than hearing individuals. However, the most interesting behavioural results showed that there is something very different in the makeup of the visual fields of the deaf and hearing participants. The hearing participants’ reaction time slowed down when the targets were on the edges of the visual field but the deaf participant’s reactions stayed equally fast.  This suggests that the deaf people are able to process detailed information from all across the visual field equally effectively, and aren’t as hampered by peripheral vision as their hearing counterparts.

Bottari, D., Caclin, A., Giard, M., & Pavani, F. (2011). Changes in Early Cortical Visual Processing Predict Enhanced Reactivity in Deaf Individuals PLoS ONE, 6 (9) DOI: 10.1371/journal.pone.0025607