Asymmetric Spatial Frequency Tuning of Motion Mechanisms in Human Vision Revealed by Masking

Abstract

PURPOSE.To investigate the spatial frequency selectivity of the human motion system by using the technique of visual masking. METHODS. Modulation-depth thresholds for identifying the direction of a sinusoidal test pattern were measured over a range of spatial frequencies (0.25-4 cyc/deg) in the absence and presence of a temporally jittering mask. RESULTS. At the lowest test frequency (0.25 cyc/deg), maximum masking occurred when the test and mask shared the same spatial frequency, decreasing as the difference in spatial frequency between the test and mask increased. However, as test spatial frequency increased, maximum masking began to shift to when the mask was presented at ϳ1 octave below the test spatial frequency. Control experiments demonstrated that the asymmetric masking functions at higher test spatial frequencies was not affected by mask amplitude nor was it an effect of speed. The results confirmed that the peak at 1 octave from the test still occurred when the potential for off-frequency looking was minimized by presenting two masks positioned equidistant in frequency from the test grating. Control experiments revealed, however, that the peak at 1 octave below the test was mediated by image size and/or the number of cycles presented on screen. CONCLUSIONS. These findings provide support for the notion that motion perception is mediated by band-pass, spatial-frequency-selective mechanisms. Moreover, asymmetric tuning of the masking functions may reflect asymmetric spatial frequency selectivity of the mechanisms in the human visual system that encode motion or inhibition between mechanisms tuned to different spatial frequencies. (Invest Ophthalmol Vis Sci. 2007;48:3897-3904) DOI:10.1167/iovs.06-1056 N umerous psychophysical studies that have investigated visual processing at threshold contrast levels have shown that the visual system contains banks of independent, quasilinear, band-pass filters, each tuned to a particular range of spatial frequencies. [1][2][3][4][5][6][7][8][9][10] Some of the most compelling evidence for the existence of spatial-frequency-selective mechanisms has come from masking studies. Masking effects are typically spatial frequency selective, occurring only when the test and mask patterns have similar spatial frequencies, and have been used to investigate the spatial frequency tuning of channels in the human visual system. 6,10 -13 However, nearly all of these masking studies have been concerned with the characteristics of the channels that encode spatial form, and surprisingly few have used masking to examine directly whether spatial-frequency-selective channels exist for encoding motion. Anderson and Burr 12 measured the spatial frequency, orientation, and temporal frequency selectivity of the visual motion system by using visual masking. As regards spatial frequency selectivity, masking was measured over a range of test spatial frequencies from 0.06 to 30 cyc/deg, with and without a superimposed high contrast, temporally jittering mask. Masking was maximum when test and mask ...

Visual adaptation reveals asymmetric spatial frequency tuning for motion

“…This illustrates well the progressively asymmetrical nature of the MAE tuning functions at the highest adaptation frequencies tested. Interestingly, the masking data of Hutchinson and Ledgeway (2007) exhibit an almost identical pattern to the MAE data of the present study, when the masking peak is plotted as a function of the spatial frequency of the drifting test grating (Figure 3b).…”

“…Although masking and adaptation are undoubtedly complex phenomena and the processes underlying each may be very different, it is striking that when the MAE peak is plotted as a function of the adaptation spatial frequency and the masking peak of Hutchinson and Ledgeway (2007) is plotted as a function of the test spatial frequency, an almost identical relationship emerges (Figure 3). Although the asymmetry in spatial tuning appears superficially to be in a totally opposite direction for masking and adaptation, this is not actually the case, but simply reflects a fundamental difference in the testing protocols employed in the two experiments.…”

“…(a) MAE peak (octaves from adaptation spatial frequency) plotted as a function of adaptation spatial frequency. (b) Masking peak, estimated by fitting Equation 1 to the data ofHutchinson and Ledgeway (2007), plotted as a function of test spatial frequency. Error bars represent ±1 SEM.…”

Short-latency ocular following responses to motion stimuli are strongly affected by temporal modulations of the visual content during the initial fixation period

“…However, this finding mimics similar observations made in earlier MAE experiments ( Ledgeway & Hutchinson, 2009 ; von Grunau & Dube, 1992 ); although in these latter studies the mismatch only developed for higher SF adapting stimuli. Hutchinson and Ledgeway (2007) observed similar phenomenon while measuring the SF tuning of motion detection mechanisms using the technique of visual masking. In those experiments, the mismatch was found with large stimuli (20 × 20 degrees, close to stimulus size in our study as well), but not with small ones (2.5 × 2.5 degrees).…”

Endogenous attention biases transformational apparent motion based on high-level shape representations

“…Extensive literature has shown that first-order and second-order stimuli can be processed by different mechanisms that exhibit distinct spatial tuning properties and temporal dynamics ( Ledgeway & Smith, 1994 , 1997 ; Allen & Derrington, 2001 ; Ledgeway & Hutchinson, 2005 ; Bressler & Whitney, 2006 ; Hutchinson & Ledgeway, 2007 ; Pavan & Mather, 2008 ; Pavan et al., 2009 ). Some second-order stimuli seem to drive low-level motion processes ( Johnston, McOwan, & Buxton, 1992 ; Lu & Sperling, 1999 ) whereas others drive high-level (feature-tracking) motion systems, like those that respond to apparent motion which also show meta-featural responses ( Cavanagh, Arguin, & von Grünau, 1989 ).…”