Journal of Vision (2014) 14(5):1, 1–27 http://www.journalofvision.org/content/14/5/1 1 A moving-barber-pole illusion Department of Cognitive Sciences, Peng Sun University of California Irvine, Irvine, CA, USA $ Department of Cognitive Sciences, Charles Chubb University of California Irvine, Irvine, CA, USA $ Department of Cognitive Sciences, George Sperling University of California Irvine, Irvine, CA, USA $ In the barber-pole illusion (BPI), a diagonally moving stream concerns the assessment of spatial relationships, grating is perceived as moving vertically because of the such as motion and location processing, and the other shape of the vertically oriented window through which it is concerns attributes leading to object identification, such viewed—a strong shape-motion interaction. We introduce as color and form processing (DeYoe & Van Essen, a novel stimulus—the moving barber pole—in which a diagonal, drifting sinusoidal carrier is windowed by a 1988; Maunsell & Newsome, 1987; Ungerleider & raised, vertical, drifting sinusoidal modulator that moves Mishkin, 1982). Under this view, the processing of independently of the carrier. In foveal vision, the moving- motion information should be independent from the barber-pole stimulus can be perceived as several active processing of form information. From a theoretical barber poles drifting horizontally but also as other complex perspective, motion can be computed without explicit dynamic patterns. In peripheral vision, pure vertical motion form constraints (DeYoe & Van Essen, 1988; Marr, (the moving-barber-pole illusion [MBPI]) is perceived for a 1982). Indeed, there have been successful motion models wide range of conditions. In foveal vision, the MBPI is that do not concern form information at all, yet manage observed, but only when the higher-order modulator motion is masked. Theories to explain the BPI make to explain a wide range of motion perception phenom- indiscriminable predictions in a standard barber-pole ena (Adelson & Bergen, 1985; Lu & Sperling, 1995; Van display. But, in moving-barber-pole stimuli, the motion Santen & Sperling, 1984, 1985; Watson & Ahumada, directions of features (e.g., end stops) of the first-order 1985; Wilson, Ferrera, & Yo, 1992). However, growing carrier and of the higher-order modulator are all different evidence now suggests that form information can from the MBPI. High temporal frequency stimuli viewed influence the extraction of motion information in peripherally greatly reduce the effectiveness of higher- various ways. (Badcock, McKendrick, & Ma-Wyatt, order motion mechanisms and, ideally, isolate a single 2003; Burr & Ross, 2002; Edwards & Crane, 2007; mechanism responsible for the MBPI. A three-stage motion-path integration mechanism that (a) computes Geisler, 1999; Geisler, Albrecht, Crane, & Stern, 2001; local motion energies, (b) integrates them for a limited time Kourtzi & Kanwisher, 2000; Krekelberg, Dannenberg, period along various spatial paths, and (c) selects the path Hoffmann, Bremmer, & Ross, 2003; Mather, Pavan, with the greatest motion energy, quantitatively accounts Bellacosa, & Casco, 2012; Pavan et al., 2011; Pavan, for these high-frequency data. The MBPI model also Marotti, & Mather, 2013; Ross, Badcock, & Hayes, accounts for the perceived motion-direction in peripherally 2000). The influence of form on motion perception viewed moving-barber-pole stimuli that do and do not might occur at several different motion processing exhibit the MBPI over the entire range of modulator (0–10 stages, including at a local motion sensing stage such as Hz) and carrier (2.5–10 Hz) temporal frequencies tested. V1 (Geisler et al., 2001), at a motion integration stage such as MT (Mather et al., 2012), and even at higher computational levels (Pavan et al., 2013; see Mather, Introduction Pavan, Marotti, Campana, & Casco, 2013, for a review). Form influences motion perception The barber-pole illusion It is widely accepted that the visual cortex contains Although computational theories of the influence of two segregated functional streams of processing. One form on motion perception have been formulated only Citation: Sun, P., Chubb, C., Sperlin, G. (2014). A moving-barber-pole illusion. Journal of Vision, 14(5):1, 1–27, http://www. journalofvision.org/content/14/5/1, doi:10.1167/14.5.1. doi: 10.1167/14.5.1 Received October 31, 2013; published May 1, 2014 ISSN 1534-7362 Ó 2014 ARVO Journal of Vision (2014) 14(5):1, 1–27 Sun, Chubb, & Sperling 2 Figure 1. Three ways of producing classical barber-pole displays viewed through a circular window. (The red annulus surrounding the window is actually opaque and contiguous with the background; it is illustrated as being partially transparent to reveal how the displays are created.) (a) View a real barber pole behind a circular window. The cylinder on which the stripes are painted rotates around a vertical axis. Although the real motion in the image plane is purely horizontal, the stripes appear to move vertically upwards. (b) Either on a computer monitor or with real materials, produce a rectangular aperture (the modulator) with the long side oriented vertically. Behind the rectangular aperture, move a grating (the carrier) diagonally upward to the right. Although the real motion is upward to the right, the direction of apparent motion within the aperture is upward, as in (a). (c) On a piece of white paper, produce an image of a barber pole as illustrated, i.e., a snapshot of a barber pole. Drag the snapshot vertically upwards. When a dynamic stimulus can be produced simply by moving a (nondeforming) snapshot of the stimulus, it is called a rigid translation. quite recently (e.g., Grossberg, Mingolla, & Viswana- BPI is determined by the motion of bar terminators (or than, 2001), the phenomena caused by form-motion end-stops) at the modulator boundary (Castet, Char- interaction were noted long ago. Perhaps the earliest ton, & Dufour, 1999; Fisher & Zanker, 2001; Kooi, and best-known phenomenon is the barber-pole 1993; Lide´n & Mingolla, 1998; Lorenceau et al., 1993; illusion (BPI; Wallach, 1935), in which a cylinder is Shimojo, Silverman, & Nakayama, 1989). In the end- painted with diagonal black and white stripes. When stop theories, the detection of the end-stop motion is the cylinder rotates about its axis, the stripes appear to implemented by a designated mechanism often referred move parallel to the axis (Figure 1a). In experimental as the end-stop mechanism. Motion produced by the settings, the barber-pole display is usually produced by end-stop mechanism then combines with that comput- multiplying a moving grating (the carrier) by a ed by the conventional motion mechanisms to produce rectangular modulator, so that the motion stimulus is the BPI (Tsui, Hunter, Born, & Pack, 2010). The end- enclosed within the rectangular region (Figure 1b). Like stop theory explains the BPI within a purely motion the illusion produced by a real barber pole, the (dorsal) pathway (Pack, Gartland, & Born, 2004; Pack, apparent motion direction of the translating bars is Livingstone, Duffy, & Born, 2003) and does not require parallel to the long axis of the modulator. The illusion subsequent crosstalk between form and motion pro- cannot be explained by any motion models that do not cessing streams (Mather et al., 2013). explicitly consider the shape of the spatial structure enclosing the motion signal. To account for the form- motion interaction that is implicit in the BPI would Motion-streak theories of the BPI require further elaboration of the existing motion Contrary to end-stop explanations, the BPI retains theories. We now consider previously proposed theo- when end-stop motions are in directions different from ries of form-motion interaction. the modulator’s elongated orientation (Beutter, Mulli- gan, & Stone, 1996; Castet & Wuerger, 1997). Also, the BPI is weakened substantially when the overall end-stop End-stop theories of the BPI motions are still along the modulator’s elongated Obviously, different theories on the BPI can lead to orientation but the modulator boundary contains different implications of the underlying neural mecha- irregular details (Badcock et al., 2003). Based on these nisms and different implications of the visual process- results, Badcock et al. (2003) proposed that the ing stages where the form-motion interaction takes modulator boundary acted like the motion streak in place. Perhaps the current predominant view is that the motion-streak models (e.g., Geisler, 1999) to produce the Journal of Vision (2014) 14(5):1, 1–27 Sun, Chubb, & Sperling 3 the features is the rigid direction of the dynamic pattern. Obviously, only a tiny subset of dynamic patterns has a unique rigid direction. A barber-pole stimulus like the one shown in Figure 1b viewed through a circular window produces exactly the same dynamic stimulus as is produced by dragging a snapshot of the same stimulus upward behind the circular window (Figure 1c). That is, the rigid direction of a barber-pole stimulus is the same as the modulator’s elongated orientation, as long as the modulator extends beyond the circular aperture. A number of different algorithms have been pro- posed to extract the rigid direction of a moving image. Figure 2. Cartoon illustration of the moving-barber-pole display. Therefore, motion models with the components that (a) A realistic scenario in which a moving truck carries three implement these algorithms (Adelson & Movshon, active barber poles. The truck and the carrier gratings inside 1982; Heeger, 1987;