In cases of bilateral auditory deprivation, there is clear evidence of an inverse relationship between performance after cochlear implantation and the length of severe to profound deafness prior to implantation (i.e. the longer the deprivation the poorer the outcome on speech perception scores with the cochlear implant). When choosing to unilaterally implant candidates, the same evidence regarding auditory deprivation is applied to each ear separately, despite the auditory system as a whole sharing a central pathway. This hypothesis is also applied to those with single-sided deafness (SSD) who have intact hearing in one ear and a severe to profound loss in the other even though the central auditory system has received direct input from the normally hearing ear. To date, no study has investigated whether the rules of auditory deprivation should still apply for SSD. Cohen and Svirsky carried out a systematic review of the SSD studies to explore this issue. They identified eight studies involving 78 subjects. Looking at each study individually did not show any trends, although combining the data did. Speech perception scores in these patients were negatively correlated with the duration of deafness, which agrees with the findings in patients with bilateral deafness. However, the study did add a caveat that the data was limited which adds uncertainty to the findings. They conclude that, if a patient with SSD is considering a cochlear implantation for the sole purpose of improving speech perception in the ear with deafness, then duration of deafness must be considered when counselling regarding outcomes. It may however be less of a consideration when implanting for other reasons, such as debilitating tinnitus.