Fig 1.
The figure provides an illustration of the Ponzo illusion in its classical configuration with two simple lines converging upwards and two horizontal lines in the centre that are identical in length but appear different.
Fig 2.
Background images in the present study.
A. Ponzo-like illusion display of a hallway with stones (textures) and walls (linear perspective cues). B. Ponzo-like illusion display of walls (linear perspective cues). C. Ponzo-like illusion display of a hallway with stones (texture gradients). D. Control background without depth cues.
Fig 3.
Illustration of stimuli and procedures that were used in the linear perspective + texture gradient background in experiments 1 and 2 (A-B and C-D, respectively). For the top standard ring block, the top standard ring was shown for 1 sec followed by an alerting sound cue that signalled the presentation of the bottom comparison ring (A and C for experiments 1 and 2, respectively). For the bottom standard ring block, the bottom standard ring was shown for 1 sec followed by an auditory alerting cue that signalled the presentation of the top comparison ring (B and D for experiments 1 and 2, respectively). In experiment 1, both the standard and comparison stimuli were presented over the same background image (A and B). In experiment 2, the comparison ring was presented outside of the background image within the grey area (C and D). The speaker symbols represent the presentation of the auditory alerting cue.
Fig 4.
Asterisks (*) represent significant differences at p < .05 after Tukey’s HSD corrections were made for multiple comparisons. Daggers (†) represent significant differences from the physical size (100 pixels) of the standard ring at p < .05 after Bonferroni corrections were made for multiple comparisons. The horizontal dashed line denotes the physical size of the standard ring. PSEs were computed from psychometric functions that best fit the data. Error bars represent the standard errors around the mean for within subjects contrasts. These error bars were calculated using procedures described by O’Brien and Cousineau [33].
Table 1.
Descriptive statistics for PSEs in experiment 1.
A series of independent samples t-tests, which were corrected for multiple comparisons using the Bonferroni method (pcorr), on the PSE values for each condition was performed between participants with (With Eye-Tacker) and without (No Eye-Tracker) eye-tracking.
Fig 5.
Fixation durations in experiment 1.
Fixation durations are the total amount of time participants gazed at an AOI across all trials for a particular condition. The asterisk (*) represents a significant difference at p < .05 after a Tukey’s HSD correction was made for multiple comparisons. Error bars represent the standard errors around the mean for within subjects contrasts. These error bars were calculated using procedures described by O’Brien and Cousineau [33].
Fig 6.
Asterisks (*) represent significant differences at p < .05 after Tukey’s HSD corrections were made for multiple comparisons. Daggers (†) represent significant differences from the physical size (100 pixels) of the standard ring at p < .05 after Bonferroni corrections were made for multiple comparisons. The horizontal dashed line denotes the physical size of the standard ring. PSEs were computed from psychometric functions that best fit the data. Error bars represent standard errors around the mean for within-subjects contrasts. These error bars were calculated using procedures described by O’Brien and Cousineau [33].
Table 2.
Descriptive statistics for PSEs in experiment 2.
A series of independent samples t-tests, which were corrected for multiple comparisons using the Bonferroni method (pcorr), on the PSE values for each condition was performed between the groups of participants with (With Eye-Tacker) and without (No Eye-Tracker) eye-tracking.
Fig 7.
Fixation durations in experiment 2.
Fixation durations are the total amount of time participants gazed at an AOI across all trials for a particular condition. The asterisks (*) represent significant differences at p < .05 after Tukey’s HSD corrections were made for multiple comparisons. Error bars represent standard errors around the mean for within subjects contrasts. These error bars were calculated using procedures described by O’Brien and Cousineau [33].