Refinements and confinements in a two-stage model of memory consolidation

Matthew Walker's model overcomes the unrefined classical concept of consolidation as a unitary process. Presently still confined in its scope to selective data mainly referring to procedural motor learning, the model nonetheless provides a valuable starting point for further refinements, which would be required for a more comprehensive account of different types and aspects of human memory consolidation.

Sleep and memory: Definitions, terminology, models, and predictions?

In this target article, Walker seeks to clarify the current state of knowledge regarding sleep and memory. Walker's review represents an impressively heuristic attempt to synthesize the relevant literature. In this commentary, we question the focus on procedural memory and the use of the term “consolidation,” and we consider the extent to which empirically testable predictions can be derived from Walker's model.

Where and When does the What system play a role in eye movement control?

This commentary focuses on Findlay & Walker's model and more specifically, on its underestimation of the role of cognitive processes in eye movement control during complex activities such as text scanning. In particular, the issue of the complexity of the subject's task/behavior is discussed to stress the importance of the link between selection for perceptual processing on the one hand, and the selection of a target for a saccade, on the other. Future models will have to account for the fact that the goal of any saccade is to bring the eyes to a relevant object and that the selection of this saccade target is closely related to object recognition.

Top-down influences on saccade generation in cognitive tasks

The theoretical framework laid out by Findlay & Walker has direct implications for central topics in research on saccades in reading and other cognitive activities and these in turn may also have implications to be considered in the context of Findlay & Walker's model. The present commentary focuses on the problem of selecting a target for a saccade. It is argued that there are indirect and direct top-down influences on this process and that direct influences are not adequately represented in Findlay & Walker's theory.

Salience, saccades, and the role of cortex

Findlay & Walker's target article proposes a model of saccade generation related to the underlying neuroscience. A problem with such models is the number of brain areas showing oculomotor function. Traditionally, therefore, models have been partial, usually concentrating either on cortex (Liu et al. 1997; Pierrot Deseilligny et al. 1995) or on the superior colliculus and brainstem circuits (Moschovakis 1994; Van Gisbergen et al. 1993). Findlay & Walker's model attempts to integrate both levels within a functional framework. To some extent it falls between two stools. For example, some functions that the authors ascribe to subcortical regions may actually occur at the cortical level.

Contextual factors in the generation of express and regular saccades

Experiments using a modified gap paradigm, where regular trials are intermingled with catch trials (trials without saccade target), demonstrate that the relative frequency of express versus regular saccades distinctly depends on catch trial frequency. More specifically, it has been shown that the probability of an express saccade depends stochastically on the type of the preceding trial, that is, on the sequence of stimuli. We discuss whether such contextual effects can be accommodated within the framework of Findlay & Walker's model.

The electromagnetic inertia of the lorentz electron

1. In a recent paper on “The Effective Inertia of Electrified Systems moving with High Speed,” G. W. Walker extends his previous investigation to the case of a perfectly conducting oblate spheroid, whose axis lies in the direction of motion, for the time being, of its centre, and whose eccentricity is equal to k , where k denotes the ratio of the speed of the centre to that of light, also for the instant under consideration. He finds (Note 1) that the longitudinal and transverse masses are equal respectively to 2 e 2 ( 1 —1/5 k 2 )/3 ac 2 (1 — k 2 ) 3/2 and 2 e 2 ( 1 —1/60 k 2 )/3 ac 2 (1 — k 3 ) 1/2 (1) instead of 2 e 2 / 3 ac 2 ( 1 - k 2 ) 3/2 and 2 e 2 / 3 ac 2 ( 1 - k 2 ) 1/2 (2) the values given by the mass formulæ of Lorentz and required by the Principle of Relativity. The method used by Walker obviates the objections raised to the assumption of quasi-stationary motion, which is necessary in the ordinary energy method of calculating the masses, but it requires special assumptions to be made at the outset both as to the constitution of the electron and as to the boundary conditions at its surface whenever definite information is needed. These assumptions obviously limit the generality of the investigation, so that it is open to the objection that Walker's model of the electron is not a suitable one, precisely because it does not agree with the Principle of Relativity.