Evaluating Letter Recognition, Flicker Fusion, and the Talbot-Plateau Law using Microsecond-Duration Flashes

Abstract

Four experiments examined the ability of respondents to identify letters that were displayed on an LED array with flashes lasting little more than a microsecond. The first experiment displayed each letter with a single, simultaneous flash of all the dots forming the letter and established the relation of flash intensity to the probability of letter identification. The second experiment displayed the letters with multiple flashes at different frequencies to determine the probability that the sequence of flashes would be perceived as fused. The third experiment displayed the letters at a frequency that was above the flicker-fusion frequency, varying flash intensity to establish the amount needed to elicit a given probability of letter identification. The fourth experiment displayed each letter twice, once at a frequency where no flicker was perceived and also with steady light emission. The intensity of each flash was fixed and the steady intensity was varied; respondents were asked to judge whether the fused-flicker display and the steady display appeared to be the same brightness. Steady intensity was about double the average flash intensity where the two conditions were perceived as being equal in brightness. This is at odds with Talbot-Plateau law, which predicts that these two values should be equal. The law was formulated relative to a flash lasting half of each period, so it is surprising that it comes this close to being correct where the flash occupies only a millionth of the total period.

Recognizing Words and Reading Sentences with Microsecond Flash Displays

“…Recent work from the present laboratory lends credibility to his claim, for not only can one see the presence of individual letters with a flash of light in the low microsecond range, but observers are able to name what letter was displayed by the ultra-brief flash [ 5 ]. This confirms the ability to register image information if flash intensity is sufficient.…”

“…e ., as continuous emission. Further, at a certain ratio of intensities a steady display will appear comparable in brightness to a 24 Hz flash sequence that has perceptually fused, with either being adequate to provide for near perfect recognition of the letters [ 5 ]. Given that individual letters can be identified under these various conditions, one wonders whether words can be named when displayed in this manner.…”

“…The first four experiments examined recognition of five-letter words using the same basic protocol as the earlier work [ 5 ]. The words were displayed on an LED array wherein each letter of the word consisted of a pattern of discrete dots, as illustrated in Fig 1 .…”

“…The words were displayed on an LED array wherein each letter of the word consisted of a pattern of discrete dots, as illustrated in Fig 1 . The letters of the prior study [ 5 ] were formed as a relatively large and dense pattern of dots, but here a fairly minimal set of dots was used for each letter. The use of smaller letter patterns was to allow words and even sentences to be written on the LED array, and a fifth experiment examined the relative salience of fused-flicker and steady display of sentences.…”

How Monitor Characteristics Affect Human Perception in Visual Computer Experiments: CRT vs. LCD Monitors in Millisecond Precise Timing Research

“…In theory, the difference in presentation methods, namely a strobing versus a static image, should be of no consequence if the light energy that falls onto the retina remains the same over the time period of one single frame. As the Talbot-Plateau law states 14 : "a flash sequence that is above the flicker-fusion threshold will be perceived as being equal in brightness to a steady stimulus when the average intensity of the former matches the intensity of the latter. " Indeed, the law holds in typical situations involving computer monitors: Photopic vision occurs when the environment is well-lit (approx.…”