The role of spatiotemporal edges in visibility and visual masking

Abstract

What parts of a visual stimulus produce the greatest neural signal? Previous studies have explored this question and found that the onset of a stimulus's edge is what excites early visual neurons most strongly. The role of inhibition at the edges of stimuli has remained less clear, however, and the importance of neural responses associated with the termination of stimuli has only recently been examined. Understanding all of these spatiotemporal parameters (the excitation and inhibition evoked by the stimulus's onset and termination, as well as its spatial edges) is crucial if we are to develop a general principle concerning the relationship between neural signals and the parts of the stimulus that generate them. Here, we use visual masking illusions to explore this issue, in combination with human psychophysics, awake behaving primate neurophysiology in the lateral geniculate nucleus of the thalamus, and optical recording in the primary visual cortex of anesthetized monkeys. The edges of the stimulus, rather than its interior, generate the strongest excitatory and inhibitory responses both perceptually and physiologically. These edges can be imaged directly by using optical recording techniques. Excitation and inhibition are moreover most powerful when the stimulus turns both on and off (what might be thought of as the stimulus's temporal edges). We thus conclude that there is a general principle that relates the generation of neural signals (excitatory and inhibitory) to the spatiotemporal edges of stimuli in the early visual system.

Visual Transients Reveal the Veridical Position of a Moving Object

“…For example, if a colour-filled stimulus is presented very briefly, the inside of the stimulus is often not perceptually filled. This is because the filling-in process cannot be completed within a short duration of time (see Macknik et al 2000). With increasing distance between edges, longer time is required for the filling-in to be completed and the vividness fades.…”

“…One important characteristic of filling-in is that the propagation of colour towards the inside of flashed edges takes time (Paradiso and Nakayama 1991). For instance, the inside of a flashed square is often perceived as less vivid than the area near the edges, or sometimes not filled-in at all (Macknik et al 2000). If the filling-in is involved in the recovery effect, the vividness of the recovered veridical position should inversely scale with the distance between flashed edges.…”

Going, going, gone: Localizing abrupt offsets of moving objects.

“…In masking, the transients of both the onset and offset of the mask elicit lateral inhibition that renders the target less visible or invisible (Macknik et al, 2000). Lateral inhibition, elicited by the offset of the moving object, might suppress the extrapolated neural representation.…”

“…Trailing behind the peak is a wake of inhibitory activity. The black dashed curve represents the transient off-signal from the sudden offset of the moving object, accompanied by lateral inhibition (Macknik et al, 2000). The peak of the transient is accurately localized and less spread out than the traveling wave.…”

Optimizing the temporal dynamics of light to human perception

“…Despite artificial lighting accounting for ∼22% of the electrical power consumption in the United States (2), light-emitting devices are not tuned to the temporal dynamics of vision. The temporal characteristics of a visual stimulus are critical to its perception (3)(4)(5)(6), although the role of stimulus duration in perceived contrast has been debated since the publication of Bloch's (7) and Broca and Sulzer's (8) contradictory studies at the turn of the 20th century (Fig. 1A).…”