Orientation tuning of contrast masking caused by motion streaks

Abstract

We investigated whether the oriented trails of blur left by fast-moving dots (i.e., "motion streaks") effectively mask grating targets. Using a classic overlay masking paradigm, we varied mask contrast and target orientation to reveal underlying tuning. Fast-moving Gaussian blob arrays elevated thresholds for detection of static gratings, both monoptically and dichoptically. Monoptic masking at high mask (i.e., streak) contrasts is tuned for orientation and exhibits a similar bandwidth to masking functions obtained with grating stimuli (∼30 degrees). Dichoptic masking fails to show reliable orientation-tuned masking, but dichoptic masks at very low contrast produce a narrowly tuned facilitation (∼17 degrees). For iso-oriented streak masks and grating targets, we also explored masking as a function of mask contrast. Interestingly, dichoptic masking shows a classic "dipper"-like TVC function, whereas monoptic masking shows no dip and a steeper "handle". There is a very strong unoriented component to the masking, which we attribute to transiently biased temporal frequency masking. Fourier analysis of "motion streak" images shows interesting differences between dichoptic and monoptic functions and the information in the stimulus. Our data add weight to the growing body of evidence that the oriented blur of motion streaks contributes to the processing of fast motion signals.

Temporal Integration of Movement: The Time-Course of Motion Streaks Revealed by Masking

“…This is consistent with previous findings on masking of gratings by moving stimuli [7], [23]. The mechanism for this is not clear, although it may relate to cross-orientation suppression [24]–[29], which is known to be isotropic (i.e., not tuned for orientation).…”

“…Geisler suggested a model in which the streak is detected by orientation-selective neurons and then combines with output from the motion system to improve directional acuity. A good deal of recent data from both psychophysics and neurophysiology supports this model [7]–[14]. It is now clear that motion streaks, although generally not perceived, do contribute to motion perception, and can interact with form processes.…”

Linear Summation of Repulsive and Attractive Serial Dependencies: Orientation and Motion Dependencies Sum in Motion Perception

“…Rapidly translating dots are known to produce orientation effects in perceptual and neural responses Apthorp et al, 2013;Geisler et al, 2001) thought to arise from temporal integration in orientation-selective neurons smearing the stimulus into oriented motion streaks. Although orientation effects from motion are easy to demonstrate (Apthorp et al, 2010;Burr and Ross, 2002;Edwards and Crane, 2007), the streaks themselves are not perceived at moderate speeds such as used here. Therefore, the only aspect of our stimulus that was consciously available at the decision level was the motion attribute and this produced a positive dependency, whereas the orientation component was not consciously available and produced a negative dependency.…”

Binocular rivalry produced by temporal frequency differences

“…Motion stimuli usually do contain form, whether complex objects or simple gratings, but even stimuli with no coherent form such as translating dots, if moving fast, can leave a pattern of elongated motion streaks due to temporal integration in neurons (Geisler, 1999; Burr and Ross, 2002). Although motion streaks are not usually perceived, they do activate orientation-tuned neurons to induce tilt illusions and aftereffects (Apthorp and Alais, 2009; Apthorp et al, 2010). In a binocular rivalry study, it was shown that “streaks” from fast moving dot patterns produce orientation-tuned rivalry suppression (Apthorp et al, 2009; Stuit et al, 2009), even though no orientation is present in the static stimulus.…”

“…The same can be said of orthogonally drifting random-dot patterns (Blake et al, 1998; van de Grind et al, 2001) because translating random-dot patterns create motion streaks (Geisler, 1999) when drifting fast, effectively transforming them into a type of grating. Recent studies have confirmed that “motion streaks” created by translating random-dot patterns do activate orientation-selective mechanisms (Apthorp et al, 2010, 2011) and do produce an orientation-specific suppression in binocular rivalry (Apthorp et al, 2009). …”