The visual system of the cat

So much of our current knowledge about the neurophysiology of vision has come from studying the visual system of the cat. Using microelectrode techniques, neurophysiologists have examined in great detail the spatial properties of receptive fields of neurons at various levels of the feline nervous system, and headway is now being made in discovering the patterns of neural connections which give rise to the remarkable degree of stimulus selectivity characteristic of these neurons. This paper reviews the major findings concerning the visual system of the normal adult cat, from optics to visual cortex, and summarizes the physiological consequences of early visual deprivation on the visual nervous system of the cat. The review concludes with remarks about the validity of generalizing from cat neurophysiology to human vision.     

On utrocular discrimination

Observers with good stereoacuity judged which eye received sine-wave grating patterns in a two-category forced-choice procedure. Large individual differences were found, but for most observers reliable discrimination was achieved at low spatial frequencies. No observer could perform the task above chance levels at high spatial frequencies. Discrimination was unaffected by retinal location, grating orientation, grating contrast, stimulus duration, or practice with feedback. Among observers who could perform the task, the following results were obtained: (1) Introduction of high spatial frequency components did not interfere with performance so long as a low spatial frequency component was present. (2) When gratings of low equal spatial frequency were presented to both eyes simultaneously at different contrast levels, observers could identify which eye received the higher contrast. (3) At low spatial frequencies, observers could distinguish monocular from binocular presentation. (4) Temporal frequency variations (counterphase flicker) influenced performance for some observers. Binocular summation and interocular transfer were unaffected by the spatial frequency variations which modulate utrocular discrimination. A new procedure for measuring stereopsis was developed which made possible comparison of utrocular discrimination with stereopsis at specific spatial frequencies. Stereopsis appeared mildly affected by spatial frequency.     

Self-limited and unlimited word usage during problem solving in two telecommunication modes

Subjects using oral modes of communication generate far more verbiage than do subjects using handwittenn or typewritten modes to solve the same problems. This study tested two alternative hypotheses to account for this disparity: (1) written modes produce a hard copy of interchanges, thereby compensating for the limitations of short-term memory and reducing the need to repeat information, and (2) talking is so easy that there is no incentive to be concise in oral modes. Two-person teams solved problems either by voice or by teletypewriter. Half the teams were given a monetary incentive to use as few words as possible. No such request was made of the control teams. Subjects in the brevity condition, regardless of the communication mode, greatly reduced verbiage with no increase in time or decrease in accuracy. Moreover, subjects in the brevity-voice condition used even fewer words than did subjects in the control-teletypewriter condition. These results, then, lend weight to the second hypothesis.     

Lehrer's fourth condition for knowing

Philosophical Studies -     

How context influences predominance during binocular rivalry

Variations in the predominance of an object engaged in binocular rivalry may arise from variations in the durations of dominance phases, suppression phases, or both. Earlier work has shown that the predominance of a binocular rival target is enhanced if that target fits well-via common color, orientation, or motion-with its surrounding objects. In the present experiments, the global context outside of the region of rivalry was changed during rivalry, to learn whether contextual information alters the ability to detect changes in a suppressed target itself. Results indicate that context will maintain the dominance of a rival target, but will not encourage a suppressed target to escape from suppression. Evidently, the fate of the suppressed stimulus is determined by neural events distinct from those responsible for global organization during dominance. To reconcile diverse findings concerning rivalry, it may be important to distinguish between processes responsible for selection of one eye's input for dominance from processes responsible for the implementation and maintenance of suppression.     

Psychophysical magic: rendering the visible 'invisible'

What are the neural correlates of conscious visual awareness? Tackling this question requires contrasting neural correlates of stimulus processing culminating in visual awareness with neural correlates of stimulus processing unaccompanied by awareness. To produce these two neural states, one must be able to erase an otherwise visible stimulus from awareness. This article describes and assesses visual phenomena involving dissociation of physical stimulation and conscious awareness: degraded stimulation, visual masking, visual crowding, bistable figures, binocular rivalry, motion-induced blindness, inattentional blindness, change blindness and attentional blink. No single approach stands above the others, but those producing changing visual awareness despite invariant physical stimulation are clearly preferable. Such phenomena can help lead us ultimately to a comprehensive account of the neural correlates of conscious awareness.