A wealth of neurophysiological data has demonstrated that visual attention can selectively enhance target representations early in the visual processing pathway. In addition, behavioural evidence tells us that the extent to which irrelevant items interfere with target processing depends on their featural similarity to the target. In this context, how does target discriminability influence temporal selection? We present results from an electrophysiology study that addresses this question by investigating the time course of the neural processes involved in target selection as target distinctiveness is varied. The results suggest that, in line with previous findings, making discrimination harder reduces the accuracy of target identification. We find that there are significant differences in the perceptual processing of the target in the two conditions, as indexed by early visual ERPs and the P3 ERP. We ground this and previous empirical evidence within a theoretical framework for understanding the mechanism of attentional selection represented in the ST2 model, a neural network model of temporal attention and working memory. By simulating both experimental conditions, we show that the model provides a convincing explanation of the pattern of experimental results, in addition to informing questions about the nature and time course of attentional selection.