Light as a true visual quantity : principles of measurement

This Technical Report summarizes visual photometric measurement methods which can provide visually meaningful assessments of light. They can be more complicated than the simple use of of a V(?)-corrected physical photometer, and in addition require some understanding of the visual system and how it works. Their advantage is that the assessment of light bears a logical relationship to the human perception of light. For photopic vision and luminances larger than several cd/m2, ordinary physical photometers corrected to V(?) give visually accurate measures for small, centrally fixed, broad-band lights. For other applications, a different luminous efficiency function should be employed. In order to utilize the appropriate function, one must either measure the spectral distribution of radiant power directly or correct the V(?) response of the photometer to the appropriate luminous efficiency. An alternative solution is to calculate mathematical formulas specifically developed for this purpose. This method is potentially the most useful since different formulas can be developed for different applications (for example, two degree or ten degree fields). It is based on established CIE data, and no additional measures need to be developed.For scotopic vision, an assessment of radiant power is made with respect to the scotopic luminous efficiency function V'(?) by means of an appropriately corrected physical photometer, by radiance measurement, or by visual photometry. In mesopic photometry, the photopic and scotopic contributions of the light must be assessed. An estimate can be obtained by combining the photopic and scotopic luminances non-linearly. A more precise measure can be obtained by using three or, still better, four quantities based on X10, Y10, Z10, and V'(?)

Young Scientists: Development of an Interactive STEM Program for Students at Vermillion “Beyond School Adventures

STEM (science, technology, engineering and mathematics) education is of increasing importance in our society. Advancements in technology, a growing need for new ideas in engineering and mathematics, and greater emphasis on science have all contributed to the renewed focus on STEM education. It is crucial that children develop an appreciation and enthusiasm for STEM at a young age. Fostering curiosity in students is a valuable investment in their personal future and the future of our world. The purpose of this thesis project was to design and implement an interactive STEM program for the after-school program, Beyond School Adventures in Vermillion, SD. This program consists of six fun, hands-on, and unique STEM activities for kindergarten and first-grade students; specifically, modules on solar heat, growing a plant, habitats, the science of sounds, engineering a communication device, and exploring plants.  Each module involves a short background presentation of the topic being explored, an opportunity for each student to do the activity, and a take-home component for extended learning and sharing of their new understanding. This project involved the development, funding, testing, revision of the modules, and presentation to the students. In future years, this project will be sustained as an outreach program of the USD Biology Club

Towards linking perception research and image quality

Image quality as a general notion relates both to elementary and to complex visual functions. In this paper we deal with a few of them, which correspond to some lines of research at our Institute. We start with threshold predictions in time and space domains by means of elementary response functions, which have been recently developed considerably, although full generalization has not yet been achieved. As to suprathreshold stimuli, the responses of subjects usually have to be scaled. Here we deal with some problems connected with scaling techniques. After a brief discussion of the applicability of notions on visual conspicuity and visual search to image quality problems, we finally discuss reading from alphanumeric displays

Temporal impulse and step responses of the human eye obtained psychophysically by means of a drift-correcting perturbation technique

Internal impulse and step responses are derived from the thresholds of short probe flashes by means of a drift-correcting perturbation technique. The approach is based on only two postulated systems properties: quasi-linearity and peak detection. A special feature of the technique is its strong reduction of the concealing effect of sensitivity drift within and between sessions. Results were found to be repeatable, even after about one year. For a 1° foveal disk at 1200 td stationary level, impulse responses of increments and decrements were found to be mirror-symmetrical. They were equal to the derivatives of the measured step responses. As a consequence the threshold of any fast-changing retinal illumination should be predictable. This will be tested in a subsequent paper. The transfer function of the system responding to a 1° stimulus shows a band-pass filter type of processing for transients, confirming quantitatively earlier findings. In contrast, a foveal point source on an extended background of 1200 td, to which impulse and step responses appear also to be linearly related, gives rise to low-pass filter action of the system

The foveal point spread function as a determinant for detail vision

A point spread function, chosen to link contrast sensitivity and stimulus dimensions, can be obtained from measured thresholds by assuming small-signal-linearity and peak detection for the visual system. To that end a special case of summation of subthreshold signals (perturbation) is used, taking specific measures against the effect of sensitivity drift. The basic assumptions are tested simultaneously and confirmed. Other provisional assumptions like radial symmetry and homogeneity were evaluated along a horizontal and a vertical meridian through the fovea. In the fovea no deviation from radial symmetry was found. The effect of inhomogeneity within the central fovea. seems to be too small to cause a significant change in the point spread function. The validity for predicting thresholds of stimuli exposing larger areas is tested. Annuli with varying radii show no significant aberration if probability summation is taken into account. Predicted disk thresholds, however, show a large discrepancy with experiment for radii larger than 2 min arc. A possible extension of the model with multiple-detection units having tuned sizes is evaluated

Effects of stimulus duration on audio-visual synchrony perception

The integration of visual and auditory inputs in the human brain occurs only if the components are perceived in temporal proximity, that is, when the intermodal time difference falls within the so-called subjective synchrony range. We used the midpoint of this range to estimate the point of subjective simultaneity (PSS). We measured the PSS for audio-visual (AV) stimuli in a synchrony judgment task, in which subjects had to judge a given AV stimulus using three response categories (audio first, synchronous, video first). The relevant stimulus manipulation was the duration of the auditory and visual components. Results for unimodal auditory and visual stimuli have shown that the perceived onset shifts to relatively later positions with increasing stimulus duration. These unimodal shifts should be reflected in changing PSS values, when AV stimuli with different durations of the auditory and visual components are used. The results for 17 subjects showed indeed a significant shift of the PSS for different duration combinations of the stimulus components. Because the shifts were approximately equal for duration changes in either of the components, no net shift of the PSS was observed as long as the durations of the two components were equal. This result indicates the need to appropriately account for unimodal timing effects when quantifying intermodal synchrony perceptio

A driving simulator study to explore the effects of text size on the visual demand of in-vehicle displays

Modern vehicles increasingly utilise a large display within the centre console, often with touchscreen capability, to enable access to a wide range of driving and non-driving-related functionality. The text provided on such displays can vary considerably in size, yet little is known about the effects of different text dimensions on how drivers visually sample the interface while driving and the potential implications for driving performance and user acceptance. A study is described in which sixteen people drove motorway routes in a medium-fidelity simulator and were asked to read text of varying sizes (9 mm, 8 mm, 6.5 mm, 5 mm, or 4 mm) from a central in-vehicle display. Pseudo-text was used as a stimulus to ensure that participants scanned the text in a consistent fashion that was unaffected by comprehension. There was no evidence of an effect of text size on the total time spent glancing at the display, but significant differences arose regarding how glances were distributed. Specifically, larger text sizes were associated with a high number of relatively short glances, whereas smaller text led to a smaller number of long glances. No differences were found in driving performance measures (speed, lateral lane position). Drivers overwhelmingly preferred the ‘compromise’ text sizes (6.5 mm and 8 mm). Results are discussed in relation to the development of large touchscreens within vehicles