Training improves visual processing speed and generalizes to untrained functions

Abstract

Studies show that manipulating certain training features in perceptual learning determines the specificity of the improvement. The improvement in abnormal visual processing following training and its generalization to visual acuity, as measured on static clinical charts, can be explained by improved sensitivity or processing speed. Crowding, the inability to recognize objects in a clutter, fundamentally limits conscious visual perception. Although it was largely considered absent in the fovea, earlier studies report foveal crowding upon very brief exposures or following spatial manipulations. Here we used GlassesOff's application for iDevices to train foveal vision of young participants. The training was performed at reading distance based on contrast detection tasks under different spatial and temporal constraints using Gabor patches aimed at testing improvement of processing speed. We found several significant improvements in spatio-temporal visual functions including near and also non-trained far distances. A remarkable transfer to visual acuity measured under crowded conditions resulted in reduced processing time of 81 ms, in order to achieve 6/6 acuity. Despite a subtle change in contrast sensitivity, a robust increase in processing speed was found. Thus, enhanced processing speed may lead to overcoming foveal crowding and might be the enabling factor for generalization to other visual functions.

Figure 1

Improvement of contrast sensitivity and masking effects following training: (a) Example of a single Gabor target used in the experiments. (b) Example of lateral masking with different target-mask separations used in the experiments. The lateral masking consisted of a target in the presence of two collinear flankers. (c) Sensitivity to an isolated Gabor target in log units (y axis) against the spatial frequency (x axis). (d) Sensitivity in log units to a target under the lateral masking condition (y axis) against a target-mask separation in λ (wavelengths) units (x axis). Red lines and filled diamonds denote the results before training and the blue lines and filled circles denote the results after training. (e) Threshold elevation (sensitivity of the target under masking conditions (see d) normalized by sensitivity to the target alone (see c)) in log units. We found significant post-training improvements in (c) and (d) but not in (e). Error bars denote the standard error of the mean (n = 14).

Figure 2

Reduction of temporal (backward) masking effects following training: (a) Example of the stimuli; the backward masking consisted of a target and two collinear flankers followed by another two collinear flankers presented after varying times (ISIs). Target detection threshold in log units (y axis) against an inter-stimulus interval (ISI, x axis). (b) Detection thresholds of the target under the backward masking conditions. (c) Threshold elevation (threshold of the target under the backward masking conditions normalized to the threshold without backward masking). Red lines and filled diamonds denote the results before training and the blue lines and filled circles denote the results after training. The post-training results for the short inter-stimulus intervals (ISI) of 60 and 90 ms significantly improved. Error bars denote the standard error of the mean (n = 14).

Figure 3

Reduced crowding and improved processing speed following training: (a) Stimulus example; E target (center) surrounded by E masks. (b) Visual acuity (VA) under crowded conditions in logMAR units (a minimal angle of resolution, y axis) as a function of the presentation time (x axis) in the pre-training (first) and post-training (second) testing sessions for the training and control groups. VA of the smallest target is presented in logMAR units. The zero line denotes a VA of 6/6 (a log minimal angle of 1). The training group is denoted by solid lines and circles. The control group is denoted by dashed lines and triangles. Open symbols and red lines stand for the pre-training results, and filled symbols and blue lines denote the post-training results. The control group's second testing after a break lasted as long as the training period. Following training, the trained group improved significantly for all durations, whereas the control group did not (see Results). (c) Reduced stimulus duration required to reach a VA of 6/6 (0 logMAR on the Y axis) following training. Whereas before training, the average exposure duration required to reach a VA of 6/6 was 204 ms (red bar), after training this exposure duration was reduced to 123 ms (blue bar). Error bars denote SEM (trained group: n = 14, controls: n = 19).