Seeing is believing: a demonstration of critical fusion frequency and its multidimensional nature.

CRITICAL FUSION FREQUENCY (CFF), or the flicker fusion threshold, is defined as the critical frequency above which a flickering light source appears steady to the observer (see Fig. 1). It is known to depend on a number of parameters, namely, intensity of the light source (5, 15), wavelength (color) of the light, retinal locus (11), binocular or monocular vision (9, 14), light-dark ratio of the stimulus (12), stimulus area (18), the level of central fatigue of the subject being tested (4), and age (24). CFF has been suggested as a diagnostic tool in certain nervous system disorders like Alzheimer’s disease (1, 2), multiple sclerosis (13, 19, 22), and schizophrenia (20). It has been used to assess the postoperative visual outcome of cataract surgeries (16) and to detect early visual field loss in patients with primary open-angle glaucoma (17). CFF has been used to quantify and diagnose minimal hepatic encephalopathy (10, 21). It is also used to quantify the cognitive side-effects in psychopharmacological studies (7, 23) and workplace fatigue (8). Thus a detailed knowledge of CFF will help the students interpret CFF laboratory test values that they will encounter later in their career as a physician or a medical researcher. Pedagogical methods like a didactic lecture, a classroom or a small group demonstration, students’ presentations, reading assignments in textbooks and journals, and classroom discussion can be used to teach the concept of CFF and its multifactorial dependence. We thought the students would have a better understanding, if it were taught using a lecture supplemented by a demonstration. The equipment used to estimate CFF in the past had rotating disks, arc lamps, and optics (6), and the cost of commercial equipment ranged from $200 to $2,000. Hence, a simple, low-cost, easily available electronic development board-based (Arduino Uno) (3) device was constructed for student demonstration purposes. This device was used to demonstrate 1) CFF; 2) effect of light intensity on CFF; 3) how CFF differs between monocular and binocular vision; and 4) CFF difference between the fovea and peripheral retina. The students were taught these concepts either by a combination of the didactic lecture and a demonstration (group A students) or by a didactic lecture (group B students) alone. Students’ understanding of the concepts was assessed by preand posttests. The scores in the tests were used to compare these two modes of teaching.