It has previously been shown that unilateral ablation of the whole auditory cortex in the cat disrupts the precedence effect, and also interferes with the ability of the normal animal to discriminate in the Y-maze between a single sound on one side and a double sound consisting of a signal on both left and right sides. The present work has confirmed these effects and has shown that both can be obtained with lesions confined to AI and AII. The "one-versus-two" deficit has invariably been seen in all the animals studied, but a proportion of animals do not show the precedence effect deficit. It has been confirmed that the apparent sucess of some animals can be due to the training effect of the one-versus-two paradigm, as was proposed in the earlier paper; however it has also been shown that this cannot be explanation in all cases. It has been demonstrated that cats are able to localize sound behind them with some success; turning around in the start box to reverse right and left space is therefore a possible strategy for overcoming a unilateral deficit. However, even with the head "fixed" in the forward-facing position, one animal was still able to run well above chance. The size of the lesion does not appear to be a correlate of the performance level.