Reinforcing saccadic amplitude variability

Saccadic endpoint variability is often viewed as the outcome of neural noise occurring during sensorimotor processing. However, part of this variability might result from operant learning. We tested this hypothesis by reinforcing dispersions of saccadic amplitude distributions, while maintaining constant their medians. In a first experiment we reinforced the least frequent saccadic amplitudes to increase variability, and then reinforced the central part of the amplitude distributions to reduce variability. The target was placed at a constant distance from the fovea after the saccade to maintain the postsaccadic visual signal constant and an auditory reinforcement was delivered depending on saccadic amplitude. The second experiment tested the effects of the contingency. We reinforced high levels of variability in 4 participants, whereas 4 other participants were assigned to a yoked control group. On average, saccadic amplitude standard deviations were doubled while the medians remained mostly unchanged in the experimental participants in both experiments, and variability returned to baseline level when low variability was reinforced. In the control group no consistent changes in amplitude distributions were observed. These results, showing that variability can be reinforced, challenge the idea of a stochastic neural noise. We instead propose that selection processes constrain saccadic amplitude distributions.     

Van Inwagen’s modal skepticism

In this paper, the author defends Peter van Inwagen’s modal skepticism. Van Inwagen accepts that we have much basic, everyday modal knowledge, but denies that we have the capacity to justify philosophically interesting modal claims that are far removed from this basic knowledge. The author also defends the argument by means of which van Inwagen supports his modal skepticism, offering a rebuttal to an objection along the lines of that proposed by Geirrson. Van Inwagen argues that Stephen Yablo’s recent and influential account of the relationship between conceivability and possibility supports his skeptical claims. The author’s defence involves a creative interpretation and development of Yablo’s account, which results in a recursive account of modal epistemology, what the author calls the “safe explanation” theory of modal epistemology.     

A problem for contrastivist accounts of knowledge

This paper raises a problem for contrastivist accounts of knowledge. It is argued that contrastivism fails to succeed in providing a modest solution to the sceptical paradox—i.e. one according to which we have knowledge of a wide range of ordinary empirical propositions whilst failing to know the various anti-sceptical hypotheses entailed by them—whilst, at the same time, retaining a contrastivist version of the closure principle for knowledge.     

Reflections on <Emphasis Type="Italic">reflective knowledge</Emphasis>

In his volume reflective knowledge, Ernest Sosa offers an account of knowledge, an argument against internalist foundationalism, and a solution to the problem of easy knowledge. This paper offers challenges to Sosa on each of those three things.     

Memory and identity

Among the many topics covered in Sven Bernecker’s impressive study of memory is the relation between memory and personal identity. Bernecker uses his grammatical taxonomy of memory and causal account to defend the claim that memory does not logically presuppose personal identity and hence that circularity objections to memory-based accounts of personal identity are misplaced. In my comment I investigate these claims, suggesting that the relation between personal identity and memory is more complicated than Bernecker’s analysis suggests. In particular, I argue (1) that while he shows that some memories do not presuppose personal identity he fails to show that those that are appealed to in memory-based accounts of personal identity do not, and (2) that the features of his view that allow him to define memory without reference to personal identity also obscure important features of memory that must be part of a complete account.