Showing papers on "Accommodation published in 1980"

The development of visual accommodation during early infancy.

Abstract: 4 experiments were conducted concerning the development of visual accommodation in 1- to 3-month-old infants. In experiments 1 and 2 dynamic retinoscopy was used to measure accomodation responses at 3 stimulus distances. The results of experiment 1 revealed better accommodative capability from 1 to 3 months than reported originally. The procedure of experiment 2 was somewhat different but the results confirmed those of experiment 1. In experiment 3, accommodative responses at 7 stimulus distances were carefully measured in a small number of infants. These data provided estimates of the shape of infants' accommodation functions. In experiment 4, we used infrared photography to measure infants' pupil diameters while they viewed the stimuli of experiments 1 and 2. 2 simple hypotheses of the developmental mechanisms which underlie early accommodative development were considered. First, development of the motor component of the accommodative system might determine accommodative development. Second, development of the sensory component of the accommodative system might determine the observed development. The first hypothesis was tentatively rejected because it is inconsistent with some clinical findings. Evaluation of the second hypothesis involved calculating infants' depth of focus. We used those depth-of-focus values to predict how well infants of different ages should accommodate if their only limitation were in the sensory component of the accommodative system. The agreement between those predictions and observed accommodation was excellent, suggesting that changes in depth of focus in the first 3 months are largely responsible for growth in accommodation. The theoretical implications of this finding are discussed.

Accommodation, convergence, and distance perception in low illumination.

Abstract: The role of oculomotor adjustments for distance perception in dim light was investigated while preserving the natural interactions between accommodation and convergence. The results show that perceived distance in the dark is biased toward an intermediate value that is correlated with the vergence adjustment assumed in darkness but unrelated to the dark focus of accommodation. A subsequent experimient showed that short-term adaptation to base-out prisms and negative lenses of corresponding strength affects perceived distance and dark convergence but has no influence on the dark focus of accommodation. These findings were interpreted as indicating that convergence is a more important distance cue than accommodation under low illumination and that the physiological resting states of convergence and accommodation are relatively independent.

Toward an adaptive model of the human eye

Abstract: A model of the human eye is presented with the crystalline lens treated as having a gradient-index structure. By defining an accommodation index I ranging from 0 (unaccommodated) to 1 (accommodated), the optical parameters of the eye in various states of accommodation may be found. The results are in agreement with experimental values.

the Effect of Cognitive Demand on Accommodation

Abstract: An optometer (infared recording retinoscope) was used to monitor the accommodation of subjects (N = 40, ages 20 to 30 years) to determine whether an increase in cognitive demand would result in an increase in the level of their accommodation. When the subjects in the experimental group (N = 20) changed from reading 2-digit numbers at 40 cm to adding the numbers, with no change in the visual stimulus, the average level of accommodation increased in 75% of the subjects--the mean level of accommodation increased 0.28 D (P < 0.01). Subjects in the control group (N = 20) showed no significant change in accommodation. The increase in accommodation is attributed to an increase in cognitive damand.

The effectiveness of a retinoscope beam as an accommodative stimulus.

Abstract: Two experiments with adult subjects and one with infant subjects showed that the beam of a retinoscope, when viewed monocularly in a dark surround, does not stimulate accommodation. In this situation, the eye assumes an intermediate focus that is correlated with the individual's intermediate dark focus or resting state of accommodation. These results provide further evidence that near retinoscopy is a useful method of refraction which controls accommodation by minimizing effective stimulation. The technique is particularly valuable for refracting infants or young children who would otherwise require cycloplegia, and it may be an effective clinical method for the correction of night myopia and related anomalies in adults.

Familiar size and linear perspective as distance cues in stereoscopic depth constancy

Abstract: Both the image size of a familiar object and linear perspective operate as distance cues in stereoscopic depth constancy. This was shown by separating their effects from the effect of the oculomotor cues by creating cue conflicts between either the familiar size cue or linear perspective, on the one hand, and accommodation and convergence, on the other. In the case of familiarsize, this cue was used deceptively. In the case of linear perspective, spectacles caused nonveridical oculomotor adjustments.

The visual accommodation response during concurrent mental activity

Abstract: The direction and magnitude of the human visual accommodation response during concurrent mental activity are investigated. Subject focusing responses to targets at distances of 0.0 D, 3.0 D and an indeterminate distance were monitored by means of an optometer during the performance of a backwards counting task and a visual imagery task (thinking near and thinking far). In both experiments a shift in accommodation towards the visual far point is observed particularly for the near target, which increases with the duration of the task. The results can be interpreted in terms of both the capacity model of Kahneman (1973) and the autonomic arousal model of Hess and Polt (1964), and are not inconsistent with the possibility of an intermediate resting position.

The demand for travel agents.

Abstract: Before a traveller takes a pleasure trip, he (she) has to plan and to make arrangements for the trip Usually he faces many options in choosing destinations, carriers, accommodation and attractions To choose wisely, he needs a wide variety of information on prices, quality, characteristics of destinations, schedules, etc After making his choices, he has to decide how best to make arrangements (eg, reservations) for the trip Some people rely on themselves to prepare and arrange their trips; others depend on the services of travel agents1 The 1976 National Travel Survey (US Travel Data Center) indicated that about 12% of all vacation trips taken by US households, and 45% of all trips taken outside the US, involved the use of travel agents in that year Surveys conducted by Hawaii Visitors Bureau showed an even greater reliance on travel agents by US mainland visitors to Hawaii In 1968, 687% of US visitors to Hawaii used travel agents to help plan and arrange their trips; by 1976, that percentage had risen to 829% (Hawaii Visitors Bureau, 1977) Two interesting questions arise Are some individuals more likely to use travel agents than others?2 Also, is the probability of the use of travel agents by a particular individual greater for some types of travel than for others? In this paper we develop a model of tourist3 demand for the services of travel agents and test it, using micro (survey) data on US mainland visitors to Hawaii collected by Hawaii Visitors Bureau in 1974 Previous studies are purely descriptive rather than analytical (ASTA, 1955; Harris, 1973-77; Time Inc, 1972) Before we begin our analysis of the demand for travel agents, we first review the function of the travel agent4

Ocular vergence-induced accommodation and its relation to dark focus.

Abstract: Two experiments were conducted in an attempt to develop an open-loop technique for assessing the influence of ocular vergence on accommodation changes. Past research had shown that a small point of light (1.2 mm in diameter) induces relatively small changes in monocular accommodation at viewing distances greater than 50 cm. However, Experiment 1 (using seven male and six female undergraduates as subjects) demonstrated that, even with a smaller light spot (.29 mm), subjects could accommodate to the stimulus at distances closer than 50 cm. It was only with a very impoverished target (.08 mm diameter), as used in Experiment 2 (in which five male and five female undergraduates served as subjects), that it was possible to present a stimulus that could induce ocular vergence without being a direct stimulus in itself for accommodation. It was also shown that ocular vergence can drive accommodation and that ocular vergence can vary systematically under conditions in which illumination is greatly reduced. In addition, both experiments showed significant relationships among dark focus and both monocular and binocular accommodation.

The role of eye accommodation in the depth perception of common toads.

Abstract: Distance estimation in prey catching was as exact in monocular toads (Bufo bufo (L.)) as in binocular ones. Application of Atropine or Miotic had no significant effect on binocular animals, whereas in monocular toads it made accurate distance estimation impossible. The accommodative state of the eye is decisive for depth estimation of monocular, but not of binocular toads.

The Relation Between Accommodation and Code Switching in a Multilingual Society: Singapore

Abstract: It appears that in multilingual societies, code switching in the two most private domains, the family domain and the friendship domain, is quite strongly linked to accommodation, particularly in transitional situations where either one or more participants leave the conversation or join it. The relationship of accommodation to pure topic related code switching can be assessed to some degree numerically by self-report of those using more than one code in any one of the domains or their sub-domains. In mixed domains, e.g. family and friends, particularly where there is a considerable difference in the verbal repertoires of the participants, strategies are at times employed to resolve the conflict arising from differing needs for accommodation. These strategies are often signalled by code switching, either spontaneous or requested. The type of strategy may differ according to the situation and its success may often depend on achieving, at least temporarily, a state approaching a quasi-similarity condition in verbal repertoires.

Best retinal focus for various fication distances in phakic and aphakic eyes.

Abstract: When an eye focuses on a distant target, it is often found that the long wavelength rays are focused on the receptors, but when the same eye looks at a target close to the eye, the green or blue rays are in focus in the retinal receptors. The authors investigated this phenomenon by means of a laser optometer to find out whether the shift in focus represented an attempt to reduce accommodative effort, or was used to aid distance judgement, or was simply a by-product of the control mechanisms. Six phakic individuals showed a shift of 50 nm over an accommodation range of 2.75 D. The single aphakic observer preferred a retinal focus within a very narrow wavelength range. The authors favor the view that the wavelength shift is an inability of the accommodative control mechanism to make a precise response to a given stimulus.