We compare luminance-contrast-masking thresholds for fully and poorly attended stimuli, controlling attention with a demanding concurrent task. We use dynamic displays composed of discrete spatiotemporal wavelets, comparing three conditions (“single,” “parallel,” and “random”). In contrast to static displays, we do not find that attention modulates the “dipper” regime for masks of low luminance contrast. Nor does attention alter direction-selective masking by multiple wavelets moving in random directions, a condition designed to isolate effects on *component motion*. However, direction-selective masking by multiple wavelets moving in parallel is significantly reduced by attention. As the latter condition is expected to excite both *component* and *pattern motion* mechanisms, this implies that attention may alter the visual representation of *pattern motion*. In addition, attention exhibits its well-known effect of reducing lateral masking between nearby spatiotemporal wavelets.

^{2}, and gamma correction combined with color bit stealing (Tyler, 1997) provided linear luminance steps of 0.07 cd/m

^{2}. Viewing was binocular (80 pixels per 1° visual angle).

_{x}, Ω

_{y}, Ω

_{t}). However, the Fourier energy of log Gabors conforms to Gaussian distributions with respect to the logarithm of spatial frequency and the logarithm of temporal frequency (as well as with respect to linear spatial direction), similar to the spatiotemporal tuning of cortical neurons (Geisler & Albrecht, 1997). The Fourier amplitude of a log Gabor wavelet is

*ω*

_{x},

*ω*

_{y},

*ω*

_{t}) are replaced by polar coordinates (

*ω*

_{r},

*θ*,

*ω*

_{t}). Ω

_{r}(cpd), Ω

_{t}(Hz), and Ω

_{θ}(°) are the peak spatial and temporal frequencies and directions, respectively; Λ

_{r}(octaves), Λ

_{t}(octaves), and Λ

_{θ}(°) are the standard deviations or bandwidth, and Φ is the phase of the wavelet.

*W*(

*x*,

*y*,

*t*) was obtained as the inverse Fourier transform of

*E*(

*ω*

_{ x},

*ω*

_{ y},

*ω*

_{ t}). The normalization of

*E*(

*ω*

_{ x},

*ω*

_{ y},

*ω*

_{ t}) was chosen such that ∣

*W*(

*x*,

*y*,

*t*)∣ takes maximal values on the order of unity. The same normalization factor was used for all the 144 wavelets.

*A*

^{+},

*A*

^{−},

*B*

^{+}, and

*B*

^{−}denote positive and negative lobes of the Fourier amplitude, which jointly determine the wavelet motion in space–time.

*A*

^{±}gives the direction dependency

*θ*,

*A*

^{+}with Ω

_{ θ}= −90° and

*A*

^{−}with Ω

_{ θ}= +90°, whereas a downward moving wavelet has

*A*

^{+}with Ω

_{ θ}= +90° and

*A*

^{−}with Ω

_{ θ}= −90°.

_{ r}= 2.5 cpd, Λ

_{ r}= 0.6 octaves, Λ

_{ θ}= 13°, Ω

_{ t}= 6.0 Hz, and Λ

_{ t}= 0.6 octaves. For comparison, the median values for area V1 neurons of macaque are Ω

_{ r}= 4.2 cpd, Λ

_{ r}= 0.72 octaves, Λ

_{ θ}= 15°, Ω

_{ t}= 7.2 Hz, and Λ

_{ t}= 1.2 octaves (Geisler & Albrecht, 1997).

*ɛ*= 3.7°. For comparison, the average diameter of central receptive fields at this eccentricity has been estimated as 0.22° in area V1 (Dow, Snyder, Vautin, & Bauer, 1981) and as 3.3° in area MT (Albright & Desimone, 1987).

*t*test on single vs. random:

*t*score = 4.73,

*df*= 8; random vs. parallel:

*t*score = 2.04,

*df*= 6).

*facilitatory*regime (or “dipper”) and an

*inhibitory*regime of mask contrast.

*P*< 1e−6,

*F*= 66.76, 42.07, and 179.55 for the single, parallel, and random configurations, respectively). An interaction (Configuration × Contrast) was significant at low (0–4%) but not at high (>4%) mask contrast (

*F*= 5.24 and

*F*= 1.03, respectively).

*low-contrast*maskers is depicted in Figures 5d–5f (filled symbols). In general, thresholds increased for relative directions 0° to 30°, reaching a plateau for relative directions of 90° and above. The particular results for each configuration mirror contrast-increment thresholds: The lowest point and the plateau level in Figures 5d–5f correspond to, respectively, the lowest point of the dipper and the absolute detection threshold in Figures 5a–5c.

*high-contrast*maskers is shown in Figures 5g–5i (filled symbols). For all configurations, the lowest thresholds were observed for a relative direction of 90°, rising to higher levels for relative directions that are less than or greater than 90°. The details of this rise suggest qualitative differences between wavelet configurations (see the Discussion section).

*asymmetry*between relative directions of 0° and 30° on the one hand and at 150° and 180°, on the other, with parallel motion masking more effectively than opponent motion. In contrast, the random wavelet configuration produced a more

*symmetric*pattern of thresholds, with comparable values at 0° and 30° and at 150° and 180°, suggesting an inhibition specific for spatial

*orientation*rather than for direction of motion. This inhibition appears weaker for maskers of identical (0°) and exactly opponent (180°) direction.

*symmetric*for random wavelets and consistently

*asymmetric*for single wavelets (results not shown).

*negative*correlation between successes (failures) in both tasks. Among a total of 91 contingency analyses, we observed no significant correlation in 87 cases and significant

*positive*correlations in 4 cases (

*χ*

^{2}measure of association). We conclude that observers did

*not*switch attention focus and that dual-task thresholds were indeed established under conditions of consistently poor attention.

*F*= 11.03 and 10.44) and almost significant (

*P*< .07,

*F*= 3.73) for random wavelets.

*F*= 127.59, 82.37, and 195.91) and attention (

*F*= 15.09, 82.56, and 111.82) and a significant interaction between contrast and attention (

*F*= 4.48, 4.28, and 11.24).

*low-contrast*maskers, poor attention elevated thresholds slightly, but the difference reached significance only in 3 of 15 conditions ( Figures 5d–5f, open symbols). Apparently, attention is of little consequence as long as the interaction between target and masker remains facilitatory.

*high-contrast*maskers ( Figures 5g–5i, open symbols). Thresholds were 33% higher on average for single wavelets, 216% higher for parallel wavelets, and 82% higher for random wavelets. A three-way ANOVA (Subject × Mask Direction × Attention) revealed significant effects of relative direction (

*F*= 39.28, 6.97, and 5.73) and attention (

*F*= 69.28, 123.52, and 80.56). For

*single*and

*parallel*wavelets, attention and relative direction interacted significantly (

*F*= 10.54 and 4.31). However, for

*random*wavelets, the attention effect was uniform across all relative directions (

*F*= 1.22).

*component motion*(Adelson & Movshon, 1982; Simoncelli & Heeger, 1998) under conditions of full and poor attention. One of our moving arrays—

*random wavelets*—sought to minimize

*pattern motion*by stimulating all directions of motion equally (cf. Figure 2d). Extensive neurophysiological evidence shows that multidirectional motion is a comparatively poor stimulus for pattern-sensitive mechanisms in visual area MT/V5 (Britten et al., 1993; Heeger et al., 1999; Qian & Andersen, 1994; Rees et al., 2000; Snowden et al., 1991). Two further moving arrays—

*single*and

*parallel wavelets*—served as controls and were expected to drive both

*component*and

*pattern motion*mechanisms well (cf. Figures 2b and 2d).

*low-contrast*masker wavelets, contrast thresholds for the detection of target wavelets were reduced, revealing

*facilitatory*interactions. In the presence of

*high-contrast*masker wavelets, contrast thresholds were elevated, reflecting

*inhibitory*interactions (Itti et al., 2000; Zenger & Sagi, 1996).

*local*interactions, such as what may arise between wavelets overlapping in space and time, from

*lateral*interactions, such as what may occur between nonoverlapping wavelets. To probe

*local*interactions, we paired overlapping target and masker wavelets and systematically varied their relative direction of motion. In the random configuration, different wavelet pairs assume different directions so that any systematic effect of relative direction must necessarily reflect

*local*interactions within each pair. To assess

*lateral*interactions, we compared multiple random wavelets, multiple parallel wavelets, and single wavelets. We expected

*lateral*interactions for multiple wavelets but not, of course, for single wavelets.

Single wavelet | Prediction | Random wavelets | Parallel wavelets | |
---|---|---|---|---|

Full attention | 6.7 ± 0.2 | 3.1 ± 0.1 | 3.7 ± 0.1 | 1.9 ± 0.2 |

Poor attention | 7.6 ± 0.2 | 3.5 ± 0.1 | 4.2 ± 0.2 | 2.6 ± 0.2 |

Single wavelet | Random wavelets | Parallel wavelets | |
---|---|---|---|

0% mask, fully attended | 100% (6.7 ± 0.2) | 100% (3.7 ± 0.1) | 100% (1.9 ± 0.2) |

16–32% mask, fully attended | 126% | 250% | 180% |

16–32% mask, poorly attended | 145% | 470% | 770% |

*reduces*lateral inhibition by nonoverlapping wavelets of high contrast. The strength of this inhibition and the degree of reduction depend on wavelet configuration (random or parallel). This interpretation—attention reduces lateral inhibition—is consistent with previous findings concerning static stimuli. It is well known that attention modulates lateral interactions between high-contrast stimuli in a configuration-dependent manner (e.g., Freeman et al., 2001; Freeman, Sagi, & Driver, 2004; Zenger et al., 2000). Inhibitory interactions are particularly affected and attention may decrease their effectiveness by a factor of 4 or more (Zenger et al., 2000).

*orientation*, not to the relative

*direction*, of target and masker wavelets (symmetric “M” shape in Figure 5i).

*orientation*selective without being

*direction*selective.

*direction*selective ( Figures 5g and 5h). This inhibition may be local or lateral or it may be both. Anderson and Burr (1985) reported a direction-selective inhibition of similar magnitude using low-pass-filtered, one-dimensional noise.

*component motion*) consists of visual filters selective for particular spatiotemporal frequencies. Our wavelets match the average filter bandwidth at this first stage. The second stage (

*pattern motion*) comprises filters selective for visual motion of a particular direction and velocity. Our random wavelet array minimizes stimulation of this second stage.