Shinya Saida

Useful visual field size for pattern perception.

The useful visual field size at each fixation in a pattern was investigated by artificially supplying various visual field sizes on a TV display. The degree of pattern perception was measured in terms of recognition memory for pictures, and the speed of processing pictures was determined as a function of field size. A serious deterioration in the perception of pictures occurred as the visual field was limited to a small area around the fovea (about 3.3° × 3.3°), processing speed becoming extremely slow. Speed increased gradually as visual field size became larger, to reach a certain level beyond which no further increase was observed. The visual field size at this asymptotic speed was called the useful visual field and was found to be about 50% of the entire pattern size. Analysis of eye-movement records demonstrated that in terms of the useful visual field, the scanning characteristics of the eye over the pattern occurred in a heavily overlapping manner to assure good perception of the pattern.

Span of recognition in reading

A question may arise when reading as to the width of the span of recognition at fixation points. A new technique was introduced to determine the size directly in a real reading situation. The visual field size was artificially narrowed, other visual functions being kept uncontrolled, and the deterioration of the reading task was investigated. An increase of the visual field size resulted in an increase of the reading rate. But no increase of the reading rate was observed beyond a certain size of the visual field, which we call the critical visual field size,Sc The value ofsc varied among subjects, ranging from 10 to 17 letters, but it was always much larger than the mean size of saccades. By regarding the critical visual field size as the span of recognition we may conclude that the reading mechanism, with its span of recognition, scans a text in a heavily overlapping manner suggesting the pre-processing of letters at the outer edge of the critical span of recognition.

Methodological caveats for monitoring binocular eye position with Nonius stimuli

Three experiments, using two sets of Nonius lines placed in a random-dot stereogram, indicated that Nonius alignment does not always reflect binocular eye position and, thus, a caveat is necessary when Nonius alignment is used to monitor binocular eye position. We found that: (a) two Nonius lines with visual line values that differed by up to 7.6 min of arc can appear aligned; (b) the two lines of each of the two Nonius sets continued to appear aligned despite a change in vergence angle of 5.9 min of arc; and (c) the Nonius alignment reflected eye position better, when the binocular dots near the Nonius lines were eliminated.

Tactile pattern recognition by graphic display: Importance of 3-D information for haptic perception of familiar objects

Haptic recognition of familiar objects by the early blind, the late blind, and the sighted was investigated with two-dimensional (2-D) and three-dimensional (3-D) stimuli produced by small tactor-pins. The 2-D stimulus was an outline of an object that was depicted by raising tactor-pins to 1.5 mm. The 3-D stimulus was a relief that was produced by raising the tactors up to 10 mm, corresponding to the height of the object. Mean recognition times for correct answers to the 3-D stimuli were faster than those for the 2-D stimuli, in all three subject groups. No statistically significant differences in percentage of correct responses between the 2-D and the 3-D stimuli were found for the late-blind and sighted groups, but the early-blind group demonstrated a significant difference. In addition, the haptic legibility for the quality of depiction of the object, without regard to whether or not the stimulus was understood, was measured. The haptic legibility of the 3-D stimuli was significantly higher than that of the 2-D stimuli for all the groups. These results suggest that 3-D presentation seems to promise a way to overcome the limitations of 2-D graphic display.

The roles of convergence and apparent distance in depth constancy with motion parallax

The question of whether motion parallax is calibrated by convergence or by apparent distance for depth perception was addressed in three experiments. In Experiment 1, a random dot parallactic display was viewed monocularly at a distance of 80 cm, and the convergence angles were set for distances of 40, 60, and 80 cm. Averaged apparent depth was not different across condi-tions. In Experiment 2, a display consisting of one surface showing dollar bills and one surface showing random dots was viewed monocularly at a distance of 80 cm. It was presented at two different apparent distances, which were manipulated by varying the size of the dollar bills. In one condition, normally sized dollar bills were presented, and in another condition, the size was reduced by 30%, The averaged apparent depth associated with the small-bill display was larger than the depth associated with the normally sized bill display. In Experiment 3, a random dot display was viewed monocularly at 120 cm. In the primary condition, the random dot display was viewed with an induction screen at 80 cm, and it was moved from side to side such that it appeared stationary and close to the plane of the induction screen. In a comparison condition, the display was viewed without the induction screen and was moving from side to side at 120 cm. In another comparison condition, the display was again viewed without the induction screen but was stationary at 120 cm. Observers adjusted the extent of motion parallax so that apparent depth was 1 cm. The mean extent of parallax was larger in the primary condition. The results show that the visual system calibrates motion parallax with apparent distance, but not directly with an oculomotor adjustment of convergence.

The Accupational Visual Field: II. Practical Aspects: The functional Visual Field in Abnormal Conditions and Its Relationship to Visual Ergonomics, Visual Impairment and Job Fitness

This second portion of the official report from the IPS Task Committee on the Functional Visual Field describes the effects of age, refractive error and its correction, ocular and neuro-ophthalmic disease, hypoxia, drugs, physical exercise, environmental lighting and noise on the functional visual field. Relationships between the functional visual field and ergonomics are also discussed, particularly with regard to driving, piloting an airplane, control tasks, illumination engineering, optical instruments, visual display units, and the design of spectacles and other devices that partially obstruct or interfere with peripheral vision. A third section examines visual field loss as a form of visual impairment, especially with regard to the definitions of visual disability, low vision and blindness, the prediction of functional capabilities, and the design of treatment regimens. Relationships between visual field properties and job fitness are discussed in a fourth section, with an emphasis on existing regulations and how they might be improved for driving, aviation and other areas. The last report section consists of technical notes pertaining to testing distance, measurement of eye and head movements, assessment of the dynamic functional visual field, and detection of visual field defects within the context of industrial medicine and automobile driver licensing requirements.

Static and Dynamic Functional Visual Fields

The size of visual field utilized by the human visual system to input information about the outside world was investigated for static and dynamic viewing conditions. In static conditions, subjects detected a target that was presented in a peripheral position while maintaining central fixation. The size depended greatly on the imposed task: a large field to detect a spot of light, a small field to distinguish a target from background noise, and a still smaller field to distinguish a target from background noise while detecting a figure in the central visual field. In the dynamic condition, subjects read sentences or perceived pictures with restricted sizes of visual field and a critical field size was determined which assured normal perceptual behaviour. The size was about 10° visual angle in both cases, which was quite large compared to the saccadic size of the eye movement, implying a need to input the entire pattern for a limited time. Reasons for such short inputting times are discussed.

Visual field size necessary for length comparison

Influence of visual field size upon acuity for comparing lengths of two lines was investigated. The visual field was effectively narrowed to any desired size by use of a TV display system. The TV screen presented a portion of the test stimulus, the position of which was controlled by the subject’s eye movement so that his fixation point always coincided with the center of the portion. The test stimulus was composed of two lines arranged horizontally, one of which had a length of 81 mm and the other a slightly different value. Sizes of the narrowed visual field were 20, 40, 70, 100, 150, and 340 mm wide. The comparison acuity dropped rapidly as the visual field was narrowed to and below 70 mm which was about the same extent as one of the two lines. The implication is that our excellent ability for length comparison is only possible when we can observe the whole line at one time.

Pupillary and cardiovascular responses to a video movie in senior human subjects

The effects of watching video movies on autonomic functions were estimated by measuring changes in pupillary and cardiovascular parameters in 10 senior subjects. The subjects looked at a series of video images (with accompanied sounds) taken during the execution of motor vehicles. The images were rear-projected on a large screen for 15 min. Pupil diameter and parameters of the light reflex were measured by an infrared pupillometer before and after the video presentation. Their electrocardiograms (ECG) and blood pressure were measured continuously. Subjects were divided into two groups depending on their values of blood pressure and fasting plasma glucose level. Subjects in Group A had blood pressures of less than 140 mm Hg and a fasting plasma glucose level of less than 7 mmol/dl (normal group). Other subjects were included in Group B (mild hypertension or diabetes mellitus group). While changes in pupillary light reflex after video viewing were minimal in the members of Group A, amplitudes of the pupillary reflex in the members of Group B varied over a significantly wide range. By the spectral analysis of cardiovascular rhythm, %LF and %HF components of blood pressure rhythm were significantly different between the two groups before video viewing. However, the ratios of frequency components before and after video viewing were not significantly different between the two groups. Our findings suggest that pupillary light reflex was less precisely controlled in subjects with mild autonomic dysfunction after prolonged audiovisual stimulation.

Use of Infrared TV Cameras Built into Head-Mounted Display to Measure Torsional Eye Movements

PURPOSE The head-mounted display (HMD) has produced conflict between visual and vestibular stimuli because the HMD image does not move with the head motion of the wearer. The HMD can show binocular parallax three-dimensional (3D) images, in which vergence and accommodation conflict. Thus, the HMD may affect the normal visual/vestibular functions. We attempted to develop a system that makes possible the measurement of torsional eye movements, vergence eye movements, and pupillary responses of the HMD wearer. METHODS Our apparatus is composed of two infrared CCD cameras installed in the HMD. Iris images produced by these cameras are analyzed by a personal computer using free software. Further, a third camera fixed on the HMD projects an image of the view as the subject sees it, via video tape recorder or frame memory to the HMD. Images can be stored, replayed, or frozen. RESULTS Our system can measure torsional eye movement with 0.20 degrees resolution every 1/30 (or 1/60) seconds even though the pupil size alternates during measurement. Binocular eye movement and pupillary response are also measured. CONCLUSION A system was developed which can be used for assessment of the effect of 3D HMD on the visual system. A third camera coupled with HMD can control visual stimulus independently of head motion (vestibular stimulus).