Generalization of perceptual learning across stimuli and tasks

Participant

Thirty-two participants with normal or corrected-to-normal vision took part in the experiments. The participants’ ages ranged from 18 to 30 years (23.6 ± 2.9, mean ± STD).

All participants passed a complete optometric eye examination and had fully corrected vision if necessary. The participants were divided into 5 experimental groups (see Table 1).

The study protocol was approved by the Internal Review Board (IRB) of Bar-Ilan University.

Informed consent was obtained from all participants.

All experimental protocols were carried out in accordance with the guidelines of the committee approving the experiments.

Participants received financial compensation for their participation. Participants were recruited via electronic advertisements and direct recruitment.

Device

The stimuli were presented at a viewing distance of 100 cm via a Windows PC computer on an EIZO 24-inch FHD with a refresh rate of 100 Hz using custom software for psychophysical experiments (PSY.) developed by Yoram S. Bonneh (2004). ) was used). The screen resolution was 1920 × 1080 pixels, giving a viewing angle of 29° × 17° (~65 pixels/degree); Gamma correction was applied. The average luminance of the screen display was 40 cd/m² when using contrast detection and BM (Gabor plaster). The black screen in TDT training was 0.3 cd/m²². All experiments were performed in a dark environment: the only ambient light came from the monitor. Participants responded using the space bar on the keyboard or computer mouse.

stimuli and task

All experiments and training were conducted under binocular conditions.

Two of the five groups completed pre- and post-tests with training in between (dummy or standard training). However, the control group completed the pre- and post-tests without training:

The test consists of two parts: In the first part, the contrast detection of a Gabor target in the center of the screen (the fixation point) was measured. The stimulus was a vertically oriented Gabor patch (GPs, Fig. 1a), 4.6 cpd, 40 ms duration. The Gabor contrast threshold was measured using an adaptive method (staircase). Target contrast increased by 0.1 log units after an error and decreased by 0.1 log units after three consecutive correct responses (3-down-1-up using the adaptive staircase procedure). In the second part, the target presentation was followed by two high-contrast (60%) collinear flankers (backward masking, BM, Fig. 1b) with a 4λ target-flanker distance and 40 ms duration. The SOA, defined as the time between the attack of the target and the flanker, was 80, 120, 160, 180, or 240 milliseconds (ms). There were 50 trials for each SOA, for a total of 300 trials, including the baseline test without a mask.

The two-time alternative forced choice (2tAFC) method was used, with the two 240 ms intervals separated by 800 ms. The participant’s task was to report the interval at which the target appeared. An acoustic signal indicated an incorrect reaction.

The target consisted of a Gabor spot with an orientation of 45°, just like the target in TDT training. At 7λ, two high contrast (90%) horizontal flankers were presented above and below the target (Fig. 2) to reduce the spatial and temporal uncertainty of the target. The target appeared in one of three locations (randomized across trials); in the center of the screen (fixation point) or in the upper left quadrant at 4° from fixation (the NW direction, the position of the texture target in TDT) or 4° away, in the lower right quadrant (the SE). Direction). The selected locations at the top left and bottom right are symmetrical and have the same sensitivity²⁹. Participants were asked to continue fixating the center during each trial. The contrast amplitude of the target was 6, 8, or 12% at the center and 16, 24, or 32% at the periphery. The contrast (3 levels) and spatial location (2 levels) of the target were randomized across trials. The stimuli were presented for 90 ms, 20 trials/condition, a total of 120 trials. A yes/no paradigm was used to test different randomly presented locations without prior cues. The hit and false alarm rates were used to calculate the sensitivity (d’) for each condition.

2-contrast detection before/after test in the center vs. at the periphery: A yes-no paradigm. The stimuli consist of an oblique (45 degree) Gabor patch target, while above and below the Gabor there are two constant high contrast (90%) orthogonal flankers. The target and the orthogonal flankers are separated by 7λ. The stimuli randomly appear in three locations (mixed depending on the trial): center, 4 degrees upper left, or 4 degrees lower right, while the participant continuously looks at the center. The contrast amplitude of the target is randomly changed to 6, 8, and 12% at the center and 16, 24, and 32% at the periphery. (A) An example of central target appearances. (b) An example of the disappearance of central goals.

In both experiments, the parameters and experimental conditions were selected after specific pilot tests, with the parameterization supported by previous studies.

TDT

TDT training

charms

The TDT stimulus (Fig. 3a) was based on and almost identical to the original by Karni and Sagi (1991). In both standard (adaptation) and dummy (reduced adaptation) conditions, a 3 × 1 diagonal bar target array was embedded in the background (a 19 × 19 array of horizontal short lines, 0.5° × 0.035°, spaced 0 .72° from each other). and with 0.05° jitter) occurring at 4° from fixation in the upper left quadrant (NW). The central target was the letter “L” or “T”. The stimulus duration was 40 ms. After a blank interval, a 100 ms mask appeared consisting of randomly aligned ˅ patterns. Power was measured as a function of SOA interval (Stimulus Onset Asynchrony: 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 260, 300, 400, 500, 600, 700 and 800 ms) . . The SOA was randomized across studies. In the dummy condition, 50% of trials consisted only of background textures without a target (i.e., “dummy” trials; see Fig. 3b). Dummy trials were randomly interleaved with the regular trials. There were 18 target trials per SOA, with 18 dummy trials per SOA added in the dummy condition. In total, there were 306 trials in the standard condition and 612 trials in the dummy condition.

TDT: (A) Schematic representation of the standard tests. The task is to distinguish between horizontal and vertical orientation of a peripheral target consisting of three diagonal lines surrounded by horizontal lines. After the target appears, a mask appears after a blank screen, called Stimulus Onset Asynchrony (SOA), which is defined as the time from the target’s appearance to the mask’s appearance. During training, the SOA changes and forms a psychometric curve that is used to estimate the threshold. (b) Schematic representation of dummy experiments. There is no texture target and only the background stimuli are displayed. The dummy trials appear randomly between test trials.

Tasks

Participants performed two tasks (“dual tasks”) on the same stimulus. The first task: There is an “L” or “T” target in the middle; The goal of the central target is to have the participant fixate on the center of the screen during the task. The participant’s task was to report the letter they saw. The second task: The participant indicated whether the three diagonal bars were arranged horizontally or vertically.

Responses were provided by two button presses: the first was for the “L” or “T” task (left click on “L,” right click on “T”); The second answer referred to the peripheral target (left click “horizontal”, right click “vertical”). Auditory feedback only indicated an incorrect response for the fixation (T/L) task (no feedback was provided for the peripheral horizontal/vertical texture task).

Before training, participants performed a practice session. The aim of this part was to familiarize participants with the experimental paradigm. The practice phase was similar to the actual training, but gradually became more difficult. There are three phases: First, the participant performed the dual tasks of the T/L task and the V/H task without masks. The number of trials was adjusted for each participant until both tasks were 100% correct (no more than ~30 trials). In the next step, there were 10 additional trials in which the mask stimulus was presented at a high SOA (800 ms). On dummy trials, participants performed the same steps as on standard trials: a T/L response and a V/H response, with the second response guessed in the absence of a recognized texture target. The third stage was very similar to the second stage, but with faster SOA trials (40–800 ms, as in full training). In the final two phases, the participant had to complete both tasks 95% correctly before they could begin training.

Participants completed the training, which consisted of four sessions spaced 2–10 days apart.

Data and statistical analysis

One-factor, two-factor, and three-factor mixed ANOVAs were conducted to test the effect of 1, 2, or 3 nominal variables (e.g., group, pre/posttest, or session) on continuous outcomes. Specifically, linear mixed-effect models were performed and an ANOVA was performed on the resulting models. Post hoc analysis was performed as pairwise comparisons defined by linear contrasts. P values ​​were adjusted for multiple testing using the Benjamini-Hochberg false discovery rate (FDR) method. The normality of the residuals and the homogeneity of the variance assumptions were assessed graphically using diagnostic plots. P values ​​less than 0.05 were considered statistically significant. The normality of the residuals and the homogeneity of the variance assumptions were assessed graphically using diagnostic plots.