Scanpaths in reading and picture viewing: computer-assisted optimization of display conditions.

A review of the literature shows that in reading and picture viewing cognitive skills play a key role along with visual acuity. Optimal processing conditions are reached only with letter and object sizes that match both cognitive skills and visual acuity. Beginning readers with normal vision need larger letters than skilled readers. In reading, eye movements step the fovea, a high-acuity region 2 degrees diameter, at the physiological pace of the visual system about 4 times per second. A simple computer-based procedure is described that determines the best acuity- and skill-matched letter (or object) sizes in the context of an optimal reading eye movement speed of 8 deg/s.

Responses of barnacle photoreceptors to high energy flashes of short duration.

In chromatic adapted barnacle median and lateral photoreceptors the two stable states of the photopigment (rhodopsin R and metarhodopsin M) were interconverted with intense, colored light flashes of 1 ms duration. Only after conversion of the red adapted photoreceptor in K+-Ringer solution with an intense flash the negative early receptor potential, ERP (of R) gradually appeared detected with an indicator flash. For the opposite conversion (blue adapted, R leads M) the gradual appearance of the positive ERP (M) was not measurable in the same time span. In artificial seawater all flash stimuli yielded--irrespective of color--the transient component of the late receptor potential (LRP). ERP results for the lateral photoreceptor are discussed in view of an existing kinetic model and an attempt is made to give an explanation which covers the new LRP transient and ERP results for both types of photoreceptor (appendix).

Visual performance and reading capacity of partially sighted persons in a rehabilitation center.

Visual acuity and reading performance of 178 partially sighted patients from a rehabilitation center were measured using a TV text display device. A linear relation was demonstrated between visual acuity and reading speed for patients with visual acuity values below 15% of the normal value. With respect to reading performance, three groups of partially sighted patients could be distinguished: (1) 25% of the patients are unable to read visually and require tactile reading aids; (2) 50% are partially sighted and require high-magnification electronic reading aids; (3) 25% can read normal text by using optical magnifying devices. There is evidence that reading performance is related to the nature of the underlying ocular problem, such as refractive anomalies, macular degeneration, or other diseases.