Conditions for view invariance in the neural response to visual symmetry

Abstract

Symmetry detection is slow when patterns are distorted by perspective, perhaps due to a time-consuming normalization process, or because discrimination relies on remaining weaker regularities in the retinal image. Participants viewed symmetrical or random dot patterns, either in a frontoparallel or slanted plane (±50°). One group performed a color discrimination task, while another performed a regularity discrimination task. We measured a symmetry-related eventrelated potential (ERP), beginning around 300 ms. During color discrimination, the ERP was reduced for slanted patterns, indexing only the remaining retinal structure. During regularity discrimination, the same ERP was view invariant, and identical for frontoparallel or slanted presentation. We conclude that normalization occurs rapidly during active symmetry discrimination, while symmetry-sensitive networks respond only to regularity in the retinal image when people are attending to other features.Descriptors: Symmetry, Event-related potentials, Sustained posterior negativity, View invariance, Perspective distortionThe two-dimensional retinal projection of an object changes dramatically as the observer adopts different vantage points. This produces novel inputs to the recognition system, but objects are nevertheless identified reliably and rapidly, and this formidable computational feat occurs unconsciously. Logothetis and Sheinberg (1996) concluded that some neurons are view invariant (firing to their preferred stimulus independent of view angle), some are view selective (firing more for some view angles), and that view invariance is more common for familiar objects than novel objects. It is also known that the neural response to faces becomes increasingly view invariant in higher visual regions (Axelrod & Yovel, 2012). Here, we measured whether the neural response to abstract visual symmetry is view invariant or view selective.Many visual systems are highly sensitive to symmetry, perhaps because it helps to identify objects against a background (Machilsen, Pauwels, & Wagemans, 2009), to achieve shape constancy (Pizlo & Stevenson, 1999), or because it indicates reproductive fitness (Tyler, 1995). Bilateral symmetry perception has been demonstrated in insects (Plowright, Evans, Leung, & Collin, 2011), birds (Møller, 1992), and humans (Julesz, 1971; Mach, 1886 Mach, / 1959. In humans, symmetry perception interacts with other figural cues (Bertamini, 2010;Treder & van der Helm, 2007), while models have been developed that extract symmetry from spatial filters (Dakin & Hess, 1997).Most psychophysical and neuroimaging researchers have used symmetric patterns in the frontoparallel plane, which produce a symmetrical retinal projection (e.g., Bertamini, Friedenberg, & Kubovy, 1997;Jacobsen & Höfel, 2003;Royer, 1981;Sasaki, Vanduffel, Knutsen, Tyler, & Tootell, 2005;Wenderoth, 1994). However, the benefits of symmetry perception presuppose the ability to recognize symmetrical objects from multiple viewpoints: After all, an observer will almost never enco...

Emergence of symmetry selectivity in the visual areas of the human brain: fMRI responses to symmetry presented in both frontoparallel and slanted planes

“…We examined responses in the same subjects and thus the same retinotopic and functionally defined areas as in the experiments conducted solely on the frontoparallel plane. The same visual areas were found to be active for slanted and frontoparallel symmetry and like Makin et al (2015), we found similar responses to these two orientations for a symmetry‐related task. The color task, however, was found to compromise responses to slanted symmetry, suggesting that normalization is interrupted when attention is directed away from symmetry and orientation.…”

“…Because asymmetry in one's conspecifics can indicate acquired or congenital disease, symmetry processing also plays a unique role in mate selection and survival. Owing to these strong evolutionary pressures, the human visual system has evolved a network of symmetry sensitive areas, emerging as early as V3 and extending across extrastriate visual cortex (Bertamini & Makin, 2014; Bona, Herbert, Toneatto, Silvanto, & Cattaneo, 2014; Chen, Kao, & Tyler, 2007; Kohler et al, 2016; Makin, Rampone, & Bertamini, 2015; Sasaki et al, 2005; Tyler et al, 2005). Recent years have seen new retinotopic areas discovered and greater consensus reached on the canonical layout of visual cortex (Amano, Wandell, & Dumoulin, 2009; Brewer, Liu, Wade, & Wandell, 2005; Larsson & Heeger, 2006; Wandell, Brewer, & Dougherty, 2005; Winawer et al, 2010).…”

“…To this end, utilizing frontoparallel stimuli, we varied both symmetry coherence and folds of symmetry while examining responses across retinotopically defined V1, V2, V3, V3AB, V7, LO1, LO2, TO1, TO2, V4, VO1, and VO2 and functionally defined lateral occipital complex (LOC), split into dorsal/posterior LOB and ventral/anterior pFs. To re‐examine the role of attention, we chose a task manipulation different to previous symmetry experiments (Sasaki, Vanduffel, Knutsen, Tyler, & Tootell, 2005), by borrowing from recent experiments that have examined changes in viewing geometry (Makin et al, 2015). Specifically, we compared responses during passive viewing to responses when a symmetry detection task was performed.…”

“…Strict retinal regularity accounts of symmetry processing however do not predict that the pattern of responses to symmetry in different planes should change when different tasks are employed. To test these predictions, Makin et al (2015) recorded symmetry‐related ERPs while participants viewed symmetry on the frontoparallel and slanted planes. Attention was directed either toward or away from the symmetry in the stimulus using regularity discrimination and color discrimination tasks, respectively.…”

“…After Makin et al (2015), we performed experiments in which we presented participants with onefold symmetrical patterns in both the frontoparallel and slanted planes (± 50°). In one experiment, participants performed a symmetry detection task, while in the other, they performed a color detection task.…”