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.

The concept of a salience map has become important for the development of theories of visual attention and saccade generation. Recent studies have shown that the frontal eye fields have all of the characteristics of a salience map.

The functional schema in the Findlay & Walker target article presents an understanding of oculomotor behavior primarily at an algorithmic level of analysis. Although such an analysis is an important first step, present knowledge of the neuroscientific substrate for oculomotor behavior is sufficiently advanced to support, if not warrant, computationally explicit models explaining how oculomotor behavior is implemented by this substrate. The literature contains a growing number of examples of this strategy, which we illustrate using our work.

Recent studies showing that pontine burst cells carry a monocular code for rapid eye movements raise questions about the organisation of signals at more central levels. Evidence that the superior colliculus may also be involved in the coding of movements in depth is reviewed. Recent work showing that the global effect is a property of refixations in 3-D space is another indication that the oculomotor systems for direction and depth are centrally coupled.

In their model, Findlay & Walker propose that where and when the eyes move is determined by two relatively independent processing streams. Whereas both saccade direction and amplitude result from a low-level visual analysis of the peripheral visual stimulation, saccade latency results mainly from higher-level processes related to processing of the central information. In the present commentary, reading eye movement data are put forward as evidence against a strict autonomy of “Where” and “When” processing streams. First, saccade direction and amplitude might be modified by high-level processes related to word identification. Second, the direction of a saccade directly affects its latency.

Findlay & Walker give voice to several common lines of thought regarding oculomotor control but do not provide sufficient detail for a critical evaluation of their theory. I argue that arbitrary spatial and temporal saccade metrics can be produced simply by manipulating the initial activation values in their model – values that the authors never specify. This lack of detail makes it difficult to anticipate the model's specific oculomotor behavior, or to compare this behavior to models opting for a more quantitative framework.

The target article retains the traditional account of saccades as conjugate eye movements. However, recent single-unit recordings of premotor cells in the saccade pathway (excitatory burster neurons [EBNs]) found that they do not encode conjugate eye velocity, but rather, monocular eye velocity. These data argue against the traditional concept of saccades as inherently conjugate. Instead, they suggest a monocular mechanism in the sensorimotor transformation stage of saccade generation. This commentary will discuss the implications of these data for the saccade generation model proposed in Findlay & Walker's target article.

Our target article discussed how emerging knowledge of the physiological processes involved in the control of saccadic eye movements provided the basis for a functional framework in which to understand the programming of such movements. The commentators raised many interesting issues in their varied responses that ranged from detailed discussion of the physiological substrate through issues of saccade control in reading. New evidence at the physiological level demonstrates that some elaborations are needed to the framework we proposed. Most clearly, the spatial selection process operates in a manner different from our suggestion of an increase in activity in the salience map. Some commentators make the interesting and welcome proposal that the functional processes we outline may in fact be implemented with an even more unified physiological substrate (continuity between collicular fixation and build-up cells) than we envisaged. Extensions to the framework are discussed involving the planning of sequential saccades, saccades made in crossmodal situations, the influences of learning and memory, and binocular saccades. We consider carefully the commentaries proposing explicit attentional and/or executive processes in the programming of saccades. We integrate the comments of researchers investigating saccade control in neurological and neuropsychiatric patients and finally discuss whether the framework can account for saccades made in the course of reading.

Colours are not the sorts of thing that are amendable to traditional forms of scientific explanation. To think otherwise is to mistake their ontology and ignore their normativity. The acquisition and use of colour categories is constrained by the logic of colour grammars.

Colour word usage within languages follows the same ordering as that proposed by Berlin and Kay between languages. This provides additional validation and support for Berlin and Kay's schema.

Saunders and van Brakel's observation that “linguistic evidence provides no grounds for the universality of basic color categories” also applies to the concept of “colour” itself. The language of “seeing” is rooted in human experience, and its basic frame of reference is provided by the universal rhythm of “light” days and “dark” nights and by the fundamental and visually salient features of human environment: the sky, the sun, vegetation, fire, the sea, the naked earth.

In reply to Wierzbicka's advocacy of semantic primitives we argue that talk of the semantic primitives (like to see) repeats the fallacies addressed in the target article at a higher level. In reply to Malcolm's plea for a Wittgensteinian grammar of colour words, we argue that he uses words like “we” and “us” too easily, falling into the trap of “silly relativism.” In reply to McManus's science of word counts, we reiterate the nineteenth-century criticism that this method is based on an illegitimate application of seemingly rigorous statistical methods.

Millikan (1998a) relies on the ability an organism may have to reidentify external objects. It is difficult to develop an account of how this might occur because the organism could make a mistake in the tokening of a concept; it could misidentify the external object. To sustain her nondescriptivism, Millikan's account of reidentification must make the link between concept and object arbitrary. However, to make mistakes possible, there must be a norm for the production of concepts. These two requirements seem to leave no room for a middle ground.

Millikan's discussion of substance concepts in terms of their information-gathering role ignores the analyses of information-based perception and action developed within the tradition of ecological psychology. Her introduction and use without definition of key Gibsonian terms such as “affordance” and “direct perception” leaves those of us investigating such concepts uncertain of the extent to which she appreciates their theoretical importance. Due recognition of the realist account of categorical perception developed by J. J. Gibson would provide mutual benefit to modern externalist philosophy as well as to experimental psychology and to those investigating the ecological approach to perception–action.

Something of the relation of my work on substance concepts to Gibsonian theories of perception–action is discussed. What historical relations tie a particular substance concept to a particular substance is discussed.