Duration discrimination of brief light flashes

The data from four experiments indicate that when Os discriminate between light flashes of different durations, for durations for which Bloch’s law has been shown to hold, their discriminations are frequently made on the temporal information available in the flashes rather than on their apparent brightness. A model for duration discrimination which specifies that discriminability depends only on the difference in duration between the two brief flashes, and is independent of their durations, is presented and applied to the data.     

Dichoptic interaction of visual structure and light flashes

Perceptual interaction between monocular flashes and different amounts of continuously visible target structure shown to the other eye was investigated. A response variable called dominance of the flashes is defined and found to be a direct function of flash intensity and an inverse function of contraocular target structure. The dominance variable is distinguished from subjective brightness of the flashes and subjective complexity of the targets. The observed effects are attributed to limited central processing capacity with increased informational load.     

Hemisphere differences and judgments of simultaneity of brief light flashes

A series of experiments was conducted to investigate the possibility of hemispheric specialization for judgments of the simultaneity of two light flashes. Right-handed subjects adjusted two light flashes until they appeared simultaneous. The comparison of measures derived from the two possible orders of the light flashes suggested that the right hemisphere of right-handed subjects performed the function of ordering visual stimuli in time. Two further experiments examined an alternative explanation, that of a left-to-right scanning mechanism, the results of which also suggested a hemisphere explanation. The results of these experiments are discussed in terms of previous research and theories which located a temporal ordering mechanism in the speech hemisphere.     

Partial integration of single electrocutaneous pulses

Psychometric functions generated by single eleetroeutaneous stimuli yielded a median coefficient of variation ( σ/μ ) of 0.23. These data are consistent with other psychometric data recently reported by us which yielded σ/μ ratios of this size. The data are discussed and related to conflicting data reported in the recent literature indicating coefficients of variation for this mode of stimulation which are only 1/3 as large. Evidence is presented for partial temporal summation (time-intensity reciprocity) for electrocutaneous stimuli ranging from 175 to 610 microseconds. The data are best fitted by the equation I x t^a = k, where a is approximately 0.57. This equation and exponent also fit summation data reported by the same authors who report finding steep psychometric functions. Clearly, then, the mechanism responsible for the very limited temporal summation found for eleetrocutaneous stimulation and the mechanism responsible for very steep psychometric functions are not identical. The discussion also includes speculation regarding possible mechanisms and suggestions for research.     

Asymmetrical retention functions for sequences of light flashes or tone bursts in the rat

In Experiment 1, rats were trained in a symbolic delayed matching-to-sample task to discriminate sample stimuli that consisted of sequences of magazine light flashes. The intertrial interval was illuminated by the houselight for Group Light, and it was dark for Group Dark. Retention functions exhibited a choose-many response bias when the delay interval was illuminated by the houselight in both groups, and no consistent response bias when the delay interval was dark. In Experiment 2, rats were trained to discriminate sample stimuli that consisted of sequences of tone bursts. During delay testing, a different tone (i.e., different frequency and location than the sample tone) was present or absent during the delay interval. The retention functions exhibited a significant choose-many bias when tone was present during the delay and a choose-few bias when tone was absent. Asymmetrical retention functions for tone burst and light flash sequences are due to the similarity between the stimulus conditions of the delay interval and the modality of the sequential event being discriminated. These results are consistent with an instructional ambiguity explanation of response biases in memory for number.     

Pigeons presented with sequences of light flashes use behavior to count but not to time

On randomly ordered trials, pigeons were presented with either a blue or a white key that flashed red for 200 ms at a fast (2 flashes/s), medium (1 flash/s), or slow (0.5 flashes/s) rate. The blue key signaled a fixed-interval (FI) schedule in which the first response after 20 s was reinforced, and the white key signaled a fixed-number (FN) schedule in which the first response after 20 flashes was reinforced. In Experiments 1 and 2, pigeons showed depressed responding to the flash on FI-cued trials and accelerated responding to the flash on FN-cued trials. When the response key was periodically blacked out in Experiments 3 and 4, counting but not timing was eliminated.     

Knowledge of results and counting of sequential light flashes by retarded and intellectually normal children.

12 adolescent retarded boys and 12 younger third-grade boys of equivalent mental age observed sequential flashes of light and made judgements of numerosity. Durations of successive flashes were 300, 500, 700, and 900 msec. in trains of 1 to 15 flashes. Over six daily sessions, subgroups receiving information about accuracy after each trial made fewer errors, and subgroups receiving none made more errors. The linear trend interaction of knowledge of results with IQ was significant, with performance of the nonretarded boys decreasing to the level of the retarded boys in the no-feedback condition. With feedback, the rate of decrease in error over sessions was similiar for both levels of IQ. The results indicate a substantial effect of knowledge of results in improving accuracy of counting by retarded and nonretarded children, this effect being relatively greater for the latter group.     

Double discrimination avoidance with a single stimulus

Four white rats were trained to avoid electric shocks by depressing a bar after the onset of a stimulus and releasing it after termination of the stimulus. All subjects acquired the behavior of holding the bar in the presence of the stimulus and releasing it in the absence of the stimulus, but one animal almost always required a "priming" shock. The others exhibited a high level of shock avoidance.     

The relationship between binocular brightness matches and luminance difference discriminability of successively presented light flashes1

Measurements of monocular ΔI and PSE as a function of the ISI between two 2-deg foveal fields successively presented to the same retinal area were obtained for two Standard durations, using the method of constant stimuli. Binocular brightness matches of the stimuli revealed that detection of a difference occurred whenever a constant difference (in log mL) in matching luminance existed. The implication of the results was that ΔI is related to the rate of change of brightness with changes in test-field luminance.     

Matching the rate of concurrent tone bursts and light flashes as a function of flash surround luminance

Subjects adjusted the rate of a repeating toneburst to match that of a concurrently flashing light, or vice versa. Flashes were viewed in luminous or wholly dark surrounds. Matches usually departed from veridical rate matches, and always were affected in the same direction by changes in surround luminance. Matches were a function of whether subjects controlled the visual or auditory stimulus; also, subjects usually reported “driving” of flash rates by auditory rates when they controlled tone rate, but not when they controlled flash rate.     

The effect of somaesthetic and acoustic stimuli on the threshold of fusion of paired light flashes in human subjects

The threshold of fusion of paired flashes of light was measured by determining the largest interval between two flashes of light at which they were reported as one and not as two flashes. When a weak electric shock to the skin was presented at the same time as the first flash, the threshold was increased compared to the threshold measured when the flashes were unaccompanied by a shock. As the interval between shock and first flash was increased up to 600 millisec, the effect diminished. A similar pattern of results was obtained using a click, instead of a shock as the additional stimulus. The effect on the two-flash threshold of varying click intensity was also studied. No retroactive effects of the shock on the two-flash threshold were observed.     

Tactile detection threshold determined with single sinusoidal mechanical pulses in the monkey skin

Tactile detection thresholds for single sinusoidal mechanical pulses increased with decreases in the frequency of the stimulus pulse (from 150 to 20 Hz) in a monkey's skin. The results correspond with those of similar electrophysiological studies.     

医患关系由“双输”到“双赢”

我国医患关系日趋紧张已是一个不争的事实,日趋恶化的医患关系使患者无奈、天使流泪、医院苦恼、政府尴尬,可谓"全盘皆输"。实现和谐医患关系达到"全赢",必须解决影响医疗服务水平的这一关键障碍,需要政府、医院、医务人员和患者多方的共同努力。     

医患关系由"双输"到"双赢"

我国医患关系日趋紧张已是一个不争的事实,日趋恶化的医患关系使患者无奈、天使流泪、医院苦恼、政府尴尬,可谓"全盘皆输".实现和谐医患关系达到"全赢",必须解决影响医疗服务水平的这一关键障碍,需要政府、医院、医务人员和患者多方的共同努力.     

Binocular detection of positive and negative flashes

Binocular forced-choice detection rates were measured under conditions where both eyes received positive flashes, both eyes received negative flashes, and one eye received a positive flash while the other received a negative flash. When both eyes received the same kind of flash, both positive or both negative, detection rates were,greater than probability summation. When one eye received a positive flash while the other received a negative flash, detection rates were near a level expected on the basis of probability summation. It is concluded that, at the level of forced-choice detection. positive and negative flashes are detected as though they were separate, independent events.     

Binocular summation in detection of contrast flashes

We studied monocular and binocular detection of foveal flashes of different contrast. When background contours were binocularly fused, detectability (d’) of binocular test flashes was, on the average, twice the detectability of monocularly presented flashes. The precise amount of binocular advantage varied with test contrast: binocular improvement exceeded full summation for low test contrast, but fell below full summation at higher test contrasts. In the absence of contours in one eye, background luminances are not expected to sum, yet binocular detection is an average of 41.5% better than monocular detection. This indicates a difference in the functional organization of the fused binocular channel and a monocular channel.