Jane Gwiazda

Stereoacuity development for crossed and uncrossed disparities in human infants.

The development of stereoacuity for crossed and uncrossed disparities was assessed by means of a preferential looking procedure in a cross-sectional sample of infants aged 2-12 months and by following a longitudinal sample over the first 8 months of life. Crossed stereoacuity was found to develop earlier but at approximately the same rate as uncrossed stereoacuity. These data are consistent with the hypothesis that there exist two binocular mechanisms, one subserving disparity detection and one for uncrossed disparity detection.

A Dynamic Relationship between Myopia and Blur-driven Accommodation in School-aged Children

Previously we reported that recently myopic children accommodated insufficiently to blur induced by negative lenses. The purpose of the present study was to relate changes in blur-driven accommodation to myopia development in children. Refractive errors and the accommodation response function (ARF) were measured in 23 myopic and 40 emmetropic children on two occasions separated by periods ranging from 6 to 12 months. Repeated measures of accommodation were made with a Canon R-1 autorefractor while negative lenses of increasing power were placed in front of the childs right eye viewing 20/100 letters at 4 m. Concomitant changes in refractive error and in accommodative function over periods of 6-12 months were found to be highly correlated in myopes (r = 0.77) but not in emmetropes (r = 0.09).

Infant visual acuity and its meridional variation

Abstract One hundred and four infants were tested using a preferential looking procedure. Results for subsets of these infants tested in three experiments were as follows: Median preference at the 75% level for vertical gratings over a homogeneous field increased monotonically from 3.0 c/deg at 17 weeks of age to 8.0 c/deg at 45 weeks of age; at the 58% level it increased from 3.7 c/deg to 11.8 c/deg. In the second experiment main axes gratings were directly paired with oblique gratings of the same spatial frequency. Results showed that the median spatial frequency at which main axes gratings were preferred over obliques (oblique effect) increased with age at a rate similar to the preference for vertical gratings. In the third experiment, vertical gratings were paired with the homogeneous field, and in separate sessions on the same infants, oblique gratings were paired with the homogeneous field. Preference thresholds for vertical gratings were similar to those for oblique gratings in very-young infants, but the preference threshold for vertical gratings increased more rapidly with age, becoming almost 1 octave greater by 11 months.

Visual acuity and its meridional variations in children aged 7–60 months

A new operant procedure was used to assess grating acuity in children aged 7-60 months. The procedure was successful for 95% of the children sampled and had high test-retest reliability. Visual acuity for main axis (horizontal and vertical) gratings improved from 6/15 at 12 months to 6/6 at 60 months. For the 7-16 month age group, preferential-looking estimates of acuity agreed well with operant estimates. Acuity for oblique gratings was approximately 1/4 octave lower than main axis acuity throughout the age range. The results suggest that the human visual system continues to develop throughout the first 5 years of life.

The Development of Vergence Does Not Account for the Onset of Stereopsis

The onset of measurable stereopsis in human infants occurs at approximately 4 months of age, directly following a period of rapid oculomotor development. The experiment reported here was designed to investigate whether the onset of stereopsis is determined solely by the onset of accurate oculomotor coordination or whether neural development in the binocular visual system is necessary. These alternatives were examined by means of a testing procedure which ensured that stimuli were presented within 1.4 deg of the horopter. That these stimuli are insensitive to errors of vergence was verified by testing thirty infants aged 6 to 10 months who were known to have stereoacuity of at least 1 min of visual angle. All but one infant retained the ability to make stereo discriminations with simulated vergence errors of up to 30 prism diopters. Results obtained from a group of forty-four infants tested longitudinally between 0 and 6 months showed a mean age of onset of stereopsis of 4.1 months. Thus, ensuring that stimuli are presented near to the horopter does not significantly alter estimates of the age of onset of stereopsis. These results suggest that neural development which is critical for the ability to make stereo discrimination must occur during the first 3 months of life.

Shifts in tonic accommodation after near work are related to refractive errors in children.

A link between changes in tonic accommodation (TA) produced by sustained near work and the development of adult‐onset myopia has been suggested in studies of young adults. Measures of TA before and after near work have been lacking in children of school age, which is the most susceptible period for the development and progression of juvenile‐onset myopia. In the present study accommodation was measured in 87 children, aged 7 to 16 years, before and after 15 minutes of video game playing. All children were refracted before testing and wore optical correction during measures of accommodation with a Canon R1 autorefractor. Most children showed initial values of TA (far focus minus dark focus) between 0.0 and 1.0D, with a mean of 0.68D. Grouped by refractive status, the myopic children initially showed 0.30D of TA, while the emmetropic children showed 0.75D and the hyperopic children showed 0.94D. After playing the video game, TA of the myopes increased by 1.15D, compared to smaller increases for the emmetropes (0.68D) and hyperopes (0.24D). Comparable values have been obtained from young adults. These results indicate that the smallest initial values of TA and the largest inward shifts in TA are found during the period of acquisition and progression of myopia, regardless of age.

Infant astigmatism and meridional amblyopia

The orientation preferences of 70 infants aged 7 to 53 weeks with significant astigmatism [1.0 or more diopters (D)] were measured using a preferential looking procedure with paired gratings. The preference data show the consequences of the blurring effects of astigmatism when these are not compensatable by accommodation. Data from infant astigmats tested with optical correction look like those of nonastigmats. We have found no evidence for the development of meridional amblyopia during the first year of life.

Infant visual acuity is underestimated because near threshold gratings are not preferentially fixated

Abstract Grating acuity thresholds obtained by the looking preference procedure have been based on the assumption that infants always prefer to look at visible patterns over blank fields. Consequently, it has been assumed that the infants preference for gratings, when compared to blank fields, would decline monotonically from 100 to 50% as the gratings increased in spatial frequency from above-threshold gratings to below-threshold gratings. Contrary to that assumption, we now find that the preference function falls significantly below 50% only to rise again at higher spatial frequencies. If preference for the grating drops significantly below 50% then the infant must be preferentially fixating the blank field which, in turn, implies discrimination of the grating. Consequently, grating acuity must exceed that based only on preferences for the grating greater than 50%.

Anisotropic resolution in children's vision.

Grating acuity was measured for 4 orientations in 111 children aged 3-8 yr. Results showed that 73% of the children had better acuity for horizontal and vertical compared to oblique gratings, 14% showed no anisotropy, and 13% had better acuity for oblique gratings. The magnitude of the oblique effect was 0.2 octaves, similar to that found in both younger children and adults.

The meaning of non-monotonic psychometric functions in the assessment of infant preferential looking acuity. A reply to Bankset al. (1982) and Telleret al. (1982)

The rapid assessment of infant visual acuity has been a topic of considerable interest in recent years. One of the most successful methods has been preferential looking (PL). The PL technique takes advantage of the fact that, given a choice between a high contrast, low spatial frequency grating and a blank field, most infants will preferentially fixate the grating. We have published evidence demonstrating that some visible gratings are not preferentially fixated but are, in fact, avoided (Held et al., 1979). We showed infant psychometric functions that were non-monotonic. As spatial frequency increased, preferential looking fell from near lOOo/, preference for the grating to significantly less than 50% before rising to levels not significantly different from 50% at high spatial frequencies. Since any significant deviation from 50% indicates an ability to see the stimulus and since these “dips” had not been previously reported in the PL literature, we suggested, on the basis of published data, that PL acuity might have been underestimated when only those points significantly above 50% were considered. We have also reported on a fast PL method that gains in reliability when these “dips” occur (Gwiazda ef al., 1980). Recently, two articles have appeared in this journal reporting failures to find “dips” below 50% in PL experiments (Teller et al., 1982: Banks et al., 1982). Both papers also question the usefulness of the fast method proposed in Gwiazda ef al. (1980). The papers raise interesting and important issues pertaining to the measurement of PL acuity. In this letter, we will address three questions raised by these articles: (I) why don’t Banks et ul. and Teller er al. find dips below 50% in their PL data? (2) In light of these results, what is the significance of the dip? (3) How do the shapes of the psychometric function and the constraints on infant testing limit the choice of psychophysical methods? Teller ef ul. (1982) report that they do not find negative preference dips in PL data from Allen (1979). In our original paper (Held ef al., 1979) we argued that their version of PL would not produce dips. Teller et al. (1982) agreed. In our version, infants are seated in a dark room facing two bright stimuli. One is a grating. At low frequencies, infants prefer the grating over the other stimulus which is a bright but blank region. If the grating is aversive, however, the infant looks at the other bright field and preferential looking for the grating drops below 50%. In the Teller version, the grating stimulus is presented on either one side or the other of a large gray field. The entire field is of the same average luminance as the grating. There is no second bright stimulus, as such. Thus, if the grating is aversive, the infant will look about at random since there is no second choice stimulus. No dip below SOY/, would be expected and none is seen. Teller et al. argue that they get preference above 50% where we get preference below 50% (see their Fig. 4). They suggest that their observers, given feedback about the actual position of the stimulus, would learn to interpret the infant’s aversion as a clue to the side containing the stimulus. We do not give the observer feedback. Their suggestion is certainly possible though Banks et al. argue that it is unlikely that an observer could change criteria rapidly enough as the stimulus changed from one spatial frequency to another. As a cause for the dip, Teller et al. suggest that “neural non-linearities” might produce a dimming of the gratings that are fixated less than 5096 of the time. Rather than an aversion for these gratings, they suggest that the infant’s behavior may reflect a simple preference for the brighter stimulus, the blank field. Banks et al. note that their method should have revealed any such effect. As it did not, they consider the explanation to be implausible. Another possible explanation for their failure to find negative values in the range of our negative values is the shallowness of the psychometric functions cited by Teller er al. Our psychometric functions are characteristically much steeper. Of the 16 infants whose functions are shown in Fig. I of Held ef al. (1979), I5 drop from better than 80’~ preference for the grating to near or below a 50%