Perceptual learning in maze discriminations

In Experiment 1, rats were trained on a discrimination between rubber- and sandpaper-covered arms of a maze after one group had been pre-exposed to these intra-maze cues. Pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made easier by adding further discriminative stimuli, when it now significantly retarded learning. In Experiment 2, rats were trained on an extra-maze spatial discrimination, again after one group, but not another, had been pre-exposed to the extra-maze landmarks. Here too, pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made substantially easier by arranging that the two arms between which rats had to choose were always separated by 135°. The results of both experiments can be explained by supposing that perceptual learning depends on the presence of features common to S+ and S-.     

Normative Practical Reasoning: Christian Pillar

In the first part I discuss the thesis, advanced by John Broome, that intentions are normatively required by all-things-considered judgments about what one ought to do. I endorse this thesis, but remain sceptical about Broome's programme of grounding the correctness of reasoning in formal relations between contents of mental states. After discussing objections to the thesis, I concentrate in the second part on the relation between rational action and rational intention. I distinguish between content-related and attitude-related reasons for propositional attitudes like believing, wanting, and intending something. The former appeal to features of the content of the propositional attitude they are reasons for, the latter would be reasons for a propositional attitude because of features of the propositional attitude as a whole, for example the feature of its being beneficial to believe or to want that p . I try to show that the common philosophical reaction to attitude-related reasons, namely to claim that they are merely content-related reasons in disguise, is mistaken. In its most extreme form such a reaction would fail to respect the first-person character of reasoning which manifests itself in, among other things, the fact that a Moore-sentence and its analogue for intentions cannot be a conclusion of reasoning. In the third part I argue that there are attitude-related reasons for intentions, and, in showing how they influence practical deliberation, I find that their existence can be rendered compatible with the thesis that it is rational to intend to do what one thinks one ought to do.     

Integration of stereo and texture cues in the formation of discontinuities during three-dimensional surface interpolation

A series of stereograms are presented which demonstrate that texture boundaries can strongly influence the perception of discontinuities between neighbouring three-dimensional (3-D) surfaces portrayed by means of stereo cues. In these demonstration figures, no stereo information is available in the immediate vicinity of the boundary between the two 3-D stereo surfaces because all texture in that region is removed in one eye's view. On the other hand, various forms of texture boundary information are provided in the resulting monocular region. This stimulus paradigm is used to explore the question: what influence does texture boundary information have on the nature of the perceived 3-D surface that is interpolated between two stimulus regions which carry stereo cues? It is shown that if a clear-cut texture boundary is present in the monocular region then this is used by the human visual system to fix the perceived location of 3-D crease and step surface discontinuities between the stereo regions. Collett (1985) explored this issue with a similar methodology and reported weak and unreliable assistance from monocular texture boundaries in helping shape 3-D stereo surface discontinuities. The strong and robust phenomena demonstrated here seem to rely on two main differences between the present stimuli and those of Collett. In the present stimuli, figurally continuous textures containing strong texture boundaries are used, together with a technique for minimising the complications, including binocular rivalry, that arise from the borders of the stimulus regions present in only one half of each stereogram.