Shape Detection of Gaborized Outline Versions of Everyday Objects

Abstract

We previously tested the identifiability of six versions of Gaborized outlines of everyday objects, differing in the orientations assigned to elements inside and outside the outline. We found significant differences in identifiability between the versions, and related a number of stimulus metrics to identifiability [Sassi, M., Vancleef, K., Machilsen, B., Panis, S., & Wagemans, J. (2010). Identification of everyday objects on the basis of Gaborized outline versions. i-Perception, 1(3), 121–142]. In this study, after retesting the identifiability of new variants of three of the stimulus versions, we tested their robustness to local orientation jitter in a detection experiment. In general, our results replicated the key findings from the previous study, and allowed us to substantiate our earlier interpretations of the effects of our stimulus metrics and of the performance differences between the different stimulus versions. The results of the detection task revealed a different ranking order of stimulus versions than the identification task. By examining the parallels and differences between the effects of our stimulus metrics in the two tasks, we found evidence for a trade-off between shape detectability and identifiability. The generally simple and smooth shapes that yield the strongest contour integration and most robust detectability tend to lack the distinguishing features necessary for clear-cut identification. Conversely, contours that do contain such identifying features tend to be inherently more complex and, therefore, yield weaker integration and less robust detectability.

Peripheral Contour Grouping and Saccade Targeting: The Role of Mirror Symmetry

“…Deviations in landing position were also smaller for contours with smaller inter-element angles, which are known to be easier to integrate [21,46,47]. This supports an interpretation of the symmetry effect in terms of grouping and not (only) saccade targeting per se.…”

“…Compared to natural scenes, contour integration stimuli are inherently cluttered as a result of the placement of many distracter elements to eliminate proximity or density cues, which is a necessary and general limitation of this paradigm that was designed to isolate grouping by good continuation. Although earlier research has shown that participants can reliably identify many everyday object shapes embedded in such Gabor stimuli when presented in central vision [46,47], it is arguably unclear how accurate or detailed participants' perception of contour shape was with our eccentrically presented shapes, and whether participants perceived the complete closed contour.…”

“…Saccadic latency did seem to properly reflect the speed or difficulty of contour integration in the sense that log latency was proportional to the contours' mean path angle in all three experiments, and contour detection difficulty is known to increase with inter-element angle (e.g., [21]; see also [46,47]). However, any influence of symmetry on saccadic latency was simply absent or at least not strong enough to show up in the results.…”

“…There is evidence that symmetry serves as a cue in classical figure-ground tasks [17,[53][54][55][56], but local shape characteristics such as the path angle [21,46,47], and global characteristics such as convexity [58] or familiarity [59] seem to be more important determinants of performance in contour integration tasks. Contour integration benefits only slightly from global symmetry in central vision [18], and the benefit is apparently further reduced or entirely absent in peripheral vision.…”

Detecting shape change: Characterizing the interaction between texture-defined and contour-defined borders

“…It should be noted that previous studies using (sampled path) objects and differing textures have been conducted (Machilsen & Wagemans, 2011;Sassi, Machilsen, & Wagemans, 2012). However, these studies have looked at gross object shape detection and identification, rather than the discrimination of subtle changes to shape.…”