In this target article we question the assumption that perception is divided into separate domains of vision, hearing, touch, taste, and smell. We review implications of this assumption for theories of perception and for our understanding of ambient energy arrays (e.g., the optic and acoustic arrays) that are available to perceptual systems. We analyze three hypotheses about relations between ambient arrays and physical reality: (1) that there is an ambiguous relation between ambient energy arrays and physical reality, (2) that there is a unique relation between individual energy arrays and physical reality, and (3) that there is a redundant but unambiguous relation, within or across arrays, between energy arrays and physical reality. This is followed by a review of the physics of motion, focusing on the existence and status of referents for physical motion. Our review indicates that it is not possible, in principle, for there to be a unique relation between physical motion and the structure of individual energy arrays. We argue that physical motion relative to different referents is specified only in the global array, which consists of higher-order relations across different forms of energy. The existence of specificity in the global array is consistent with the idea of direct perception, and so poses a challenge to traditional, inference-based theories of perception and cognition. However, it also presents a challenge to much of the ecological approach to perception and action, which has accepted the assumption of separate senses.

The global array may be a useful concept in studying behavior in a complex environment, especially in the context of dynamical systems theory. However, Stoffregen & Bardy's arguments are weakened by the conflation of sensation and perception, and by the lack of evidence for synergy between stimulus energy arrays; strong evidence places the convergence of sensory stimuli inside the head.

Based on studies with infants, we expand on Stoffregen & Bardy's explanation of perceptual motor errors, given the global array. Information pick-up from the global array is not sufficient without adequate exploratory movements and learning to support perceptually guided activity.

Stoffregen & Bardy's target article is based on the assumption that our senses' ultimate purpose is to provide us with perfect information about the outside world. We argue that it is often more important that information be available quickly than that it be perfect. Consequently our nervous system processes different aspects of information about our surrounding as separately as possible. The separation is not between the senses, but between separate aspects of our surrounding. This results in inconsistencies between judgments: sometimes because different frames of reference are used. Such inconsistencies are fundamental to the way the information is picked up, however, and hence cannot be avoided with clearer instructions to the subjects.

Stoffregen & Bardy propose an absolutist transmodal array structure model, intended to displace models of specification in all existing perceptual theories. Absolute specification of world structure in array structures, either unimodal or transmodal, may not be provable, but might be falsifiable. Absolute specification, moreover, may not be a necessary postulate in an ecological approach to understanding perception-action.

Stoffregen & Bardy suggest that the global array provides the specification that is lacking when senses are considered in isolation. This seems to beg the question of the minimum number of senses in a global array. Individuals with sensory loss manage with fewer senses, and humans manage with fewer than electric fish; so specification, if it exists, cannot require all possible senses.

Is there any ecological purpose in assuming that perception for action exists only through a global array of energy? Unlike Stoffregen & Bardy, who assume that behavior consists of movements, we would argue that behavior consists of a stable coupling between perception and action achieved through experience in an adaptive context. Determining target position in an aiming manual task and temporal control of impact movement illustrate that patterns of energy used for action are task-dependent.

Stoffregen & Bardy argue that unimodal invariants do not exist, and that only “amodal” invariants are possible. But they confuse two separate issues. Amodal invariants, we argue, do indeed exist to specify features of the environment, but not even an amodal invariant, in isolation, could specify their “presence” or “reality.”

The information required for perception may be available in the energy arrays that stimulate sensory organs but in a form not directly suitable for the planning and execution of the organism's actions in the environment. The requisite form of information is obtained, with no loss of adequate perception, by representation of sensory stimuli in frames of reference determined by internal control signals producing actions. This process seems evolutionarily advantageous but makes perception essentially non-direct, regardless of the degree of intra- or inter-modal sensory integration.

We find Stoffregen & Bardy's argument that the senses are united and that specificity exists within the global array compelling. However, this view is not entirely new and research on the development and the origins of perception in infancy, inspired by Gibson's ecological perspective, also supports their claims. The inclusion of this developmental research will strengthen and challenge some of Stoffregen & Bardy's views.

Claims made in the target article that information-that-specifies is contained in relations among structured energy arrays, considered as wholes, may well be true, but claims that information-that-specifies is only contained in irreducible relations among structured energy arrays, considered as wholes, fail to persuade, at least in the case of the blind.

We believe that the task goal in voluntary movements provides meaning to existing information sources in the environment and determines, in a dynamic way, the use and relative importance of these different sources. This task-centered meaning bridges the apparent controversy between what information is available in principle (i.e., specification), and what information is perceived.

Stoffregen & Bardy suggest that the senses are not separable. However, they have a philosophical approach rather than using direct evidence that the nervous system analyzes sensory information in a highly flexible manner.

The arguments of Stoffregen & Bardy for studying perception based on the global array are intriguing. This theory can be examined in nonhuman species using nonverbal tasks. We examine how monkeys master a skill that incorporates a two-dimensional/three-dimensional interface. We feel this provides excellent support for Stoffregen & Bardy's theory.

Stoffregen & Bardy reject the likelihood that infants are sensitive to the global array, implying that intersensory integration is not possible in early development. We argue that infants are sensitive to unimodal arrays and are able to integrate them through the active participation of their nervous system and that the observed developmental changes are due to experience and brain development.

This commentary discusses a strategy by which investigators can examine whether observers perceive properties of the global array independently of properties in individual sensory arrays. Research showing that perception of complex relationships appears to be independent of the perception of individual components is considered. Ashby and Townsend's (1986) methods for identifying perceptual independence are important tools for studying the global array.

James Gibson's theory of information, as specific to (but not necessarily “like”) its sources, is especially indebted to the study of occlusion for its core examples. In occlusion, one is “amodally” aware of hidden surfaces. Is this still too related to one modality to count as a good case for Stoffregen & Bardy?

Stoffregen & Bardy's arguments against separation of the senses fail to consider the functional differences between the kinds of information potentially available in the structured energy arrays that correspond to the traditional senses. Since most perception/action research pursues a strategy of information perturbation presupposing differential contributions from the various ambient arrays, the global array hypothesis can only be extended and tested by analyses that consider the functional aspects along which the senses can, in fact, be separated.

There is a discrepancy between Stoffregen & Bardy's concept with experimental work on human self-motion perception. We suggest an alternative: (1) higher brain centers are informed by a given sensory cue in a direct and rapid way (direct perception), and (2) this information is then used to prime and shape a more complex mechanism that usually involves several cues and processing steps (inferential).

Before one can talk about global arrays and multimodal detection, one must be clear about the concept of information: How is it different from energy and how is it detected? And can it come to specify a needed movement? We consider these issues in our commentary.