Human Psychophysics Dataset on Figure Ground Segregation in Texture Stimuli

The dataset is derived from a psychophysics experiment where 8 participants discriminated the orientation of a rectangular figure within a texture stimulus comprised of Gabor annuli. The figure region differed from the background in its contrast distribution, controlled by two independent variables: Contrast Heterogeneity and Grid Coarseness. Contrast Heterogeneity refers to the range of contrasts exhibited by Gabor annuli. In this experiment, there were five values for Contrast Heterogeneity in the figure: 0.01, 0.2575, 0.505, 0.7525, and 1. The contrast distribution of the background was always maximally heterogeneous with Contrast Heterogeneity equal to 1.  Grid Coarseness, on the other hand, refers to the scaling factor that controls the spacing between the Gabor annuli. It determines the density of the grid pattern in the background and the figure region. In this experiment, there were five values for Grid Coarseness: 1, 1.125, 1.250, 1.375, and 1.5. The experiment consisted of 9 sessions, each containing multiple blocks of trials. Each block of trials contained 25 unique stimulus conditions, defined by the combination of Contrast Heterogeneity and Grid Coarseness.

Stimuli, Tasks, and Procedure 

Each texture stimulus consisted of a full-screen irregular grid of non-overlapping Gabor annuli placed on a grey background. The Gabor annuli had a diameter of 0.7°, a spatial frequency of 5.7 cycles/degree, and a mean luminance of 60.76 Cd/m2. Embedded within this texture was a rectangular figure region located in the lower right quadrant of the screen, which differed from the rest of the texture in the contrast distribution of its annuli. For sessions 1-8, the figure center was placed at an eccentricity of (7 ± 1)° but slightly varied in terms of polar angle such that it was completely inside the lower right quadrant. For session 9 (transfer session), the figure was placed in the upper left quadrant. 

Participants were required to indicate whether the rectangular figure was oriented horizontally or vertically by pressing the right and left arrow keys, respectively. The experiment employed a two-alternative forced-choice design, in which participants had to make a decision about the orientation of the figure in each trial. Responses were given with the middle and index fingers of the right hand. In each trial, the stimulus was presented for 1000 ms or less if the participant lost fixation or provided a response. Participants were required to maintain fixation throughout the presentation of the stimulus. 

After each trial, participants received feedback on their response. If the response was correct, a green fixation point was presented for 500 ms. If the response was incorrect, a red fixation point was presented for 500 ms. 

The experiment was conducted in a dimly lit room. A chin and head-rest was used to support the participant's head and to keep eye-screen distance constant at 57 cm. Stimuli were displayed on a 19'' Samsung SyncMaster 940BF LCD monitor. Stimulus representation and response recording were performed using Psychtoolbox-3 for Matlab 64-Bit (Version 3.0.14 - Build date: Apr 6th, 2018) running on a Windows operating system. Fixation was monitored with a desktop-mounted Eyelink 1000 eye-tracker (SR Research Ltd.) with a sampling frequency of 500 Hz or 1000 Hz and a spatial resolution of <0.01° RMS. Eye-movement data were down-sampled to 250 Hz. 

Procedure for Handling Aborted Trials 

If a participant's gaze fell outside the fixation window during the fixation period preceding the stimulus, or during stimulus presentation, the trial was aborted. Aborted trials were repeated at a randomly chosen time during the experiment. 

Parametrization of the Experimental Setup 

The eye-screen distance was set to 57 cm. The stimulus presentation time was set to 1000 ms. The inter-trial interval was set to 900 ms. Each session consisted of 30 blocks, with 25 trials per block. 

Transfer Session 

The transfer session (session 9) was unique in that the rectangular figure was presented in the upper left quadrant of the screen, rather than the lower right quadrant as in sessions 1-8. This was done to test the transfer of learning to a new location. Participants were made aware of the figure displacement but were not told in which quadrant to expect it. 

Variables 

The dataset includes identifiers for each participant (SubjectID), session (SessionID), and block of trials (BlockID). For each trial, the dataset includes the condition (Condition), the contrast heterogeneity (ContrastHeterogeneity), the grid coarseness (GridCoarseness), the participant's response (IndicatedOrientation), the actual orientation of the rectangular region (ActualOrientation), and whether the participant's response was correct (Correct). The dataset also includes demographic information comprising their unique identifier (SubjectID), age (Age), and sex (Sex). 

Ethics

After receiving full information about all procedures and about the right to withdraw participation at any time, they provided written informed consent according to the Helsinki Declaration. All procedures were approved by the local Ethical Committee of the Faculty of Psychology and Neuroscience (ERCPN). Participants received
monetary reward.