On-off selectivity and asymmetry in apparent contrast: An adaptation study

Using textures composed of sparse bright/dark elements that can activate either on or off sensors selectively, Sato, Motoyoshi, and Sato (2012) reported simultaneous contrast-contrast effects tuned for contrast polarity. As with contrast-contrast effects, prolonged viewing of high-contrast stimuli reduces the perceived contrast of a subsequently presented stimulus. The present study examined whether contrast aftereffects are also selective for luminance polarity using texture patterns composed of sparse bright/dark elements. Results revealed that contrast aftereffects are selective for luminance polarity (polarity selectivity) but that adaptation aftereffects occur asymmetrically depending on the polarity of the adapter (polarity asymmetry). Polarity selectivity and asymmetry in adaptation aftereffects are reduced but not completely diminished if adapter and test stimuli are presented to separate eyes (dichoptically). Our results support the idea that suprathreshold contrast perception and its adaptational shifts are jointly determined by responses between monocular and binocular units

Eye contrast polarity is critical for face recognition by infants

Just as faces share the same basic arrangement of features, with two eyes above a nose above a mouth, human eyes all share the same basic contrast polarity relations, with a sclera lighter than an iris and a pupil, and this is unique among primates. The current study examined whether this bright-dark relationship of sclera to iris plays a critical role in face recognition from early in development. Specifically, we tested face discrimination in 7- and 8-month-old infants while independently manipulating the contrast polarity of the eye region and of the rest of the face. This gave four face contrast polarity conditions: fully positive condition, fully negative condition, positive face with negated eyes ( negative eyes ) condition, and negated face with positive eyes ( positive eyes ) condition. In a familiarization and novelty preference procedure, we found that 7- and 8-month-olds could discriminate between faces only when the contrast polarity of the eyes was preserved (positive) and that this did not depend on the contrast polarity of the rest of the face. This demonstrates the critical role of eye contrast polarity for face recognition in 7- and 8-month-olds and is consistent with previous findings for adults

Adaptive comparison matrix: An efficient method for psychological scaling of large stimulus sets.

Studies on natural and social vision often need to quantify subjective intensity along a particular dimension for a large number of stimuli whose perceptual ordering is unknown. Here, we introduce an easy experimental protocol of comparative judgments that can rank and scale subjective stimulus intensity using a comparatively small number of trials. On each trial in our protocol, the observer initially views M stimuli sampled from a space of N stimuli and selects the stimulus that elicits maximum subjective response along a given dimension (e.g., the most attractive). The selected stimulus is subsequently discarded, the observer then performs a judgment on the remaining stimuli, and the process is iterated until the last stimulus remains and a new trial begins. The method relies on sorting perceived stimulus order in the N x N comparison matrix via logistic regression and sampling the next set of M stimuli such that responses will be collected only for stimulus pairs whose expected response ratio is most informative. Numerical simulations demonstrate that this method can estimate psychological scale with a small number of responses. Psychophysical experiments confirm that the method can quickly estimate the contrast response function for gratings and the perceived glossiness of naturalistic objects. This protocol would be useful for characterizing human judgments along various dimensions, especially those with no physical image correlates such as emotional and social attributes

Attentional Modulation of Temporal Contrast Sensitivity in Human Vision

Recent psychophysical studies have shown that attention can alter contrast sensitivities for temporally broadband stimuli such as flashed gratings. The present study examined the effect of attention on the contrast sensitivity for temporally narrowband stimuli with various temporal frequencies. Observers were asked to detect a drifting grating of 0–40 Hz presented gradually in the peripheral visual field with or without a concurrent letter identification task in the fovea. We found that removal of attention by the concurrent task reduced the contrast sensitivity for gratings with low temporal frequencies much more profoundly than for gratings with high temporal frequencies and for flashed gratings. The analysis revealed that the temporal contrast sensitivity function had a more band-pass shape with poor attention. Additional experiments showed that this was also true when the target was presented in various levels of luminance noise. These results suggest that regardless of the presence of external noise, attention extensively modulates visual sensitivity for sustained retinal inputs

Effect on the slope of psychometric function.

<p>(a) Examples of psychometric functions for the peripheral grating detection. The upper panel shows the results for the static grating (0 Hz) and the lower panel the results for the fast drifting grating (26.7 Hz). The solid curves are the psychometric functions for the single-task mode, and the red dashed curves are those for the dual-task mode. (b) Slope of psychometric functions plotted as a function of the grating temporal frequency. The open circles shows the results for the single-task mode, and the red circles the results for the dual-task mode. Error bars are +−1 s.e.m. across observers. (c) Contrast sensitivity defined with different performance criteria; the red symbols for d′ = 1.0, purple symbols for d′ = 2.0, and blue symbols for d′ = 3.0. The lower panel shows the ratio in the sensitivity between the two task modes. Error bars are +−1 s.e.m. across observers.</p

Sensitivity to Acceleration in the Human Early Visual System

It is widely believed that the human visual system is insensitive to acceleration in moving stimuli. This notion is supported by evidence that detection sensitivity for velocity modulation in moving stimuli is a lowpass function of the velocity modulation's temporal frequency. However, the lowpass function might be a mixture of detection by attention-based tracking and low-level mechanisms sensitive to acceleration. To revisit the issue of acceleration perception in relation to attentive tracking, we measured detection sensitivities for velocity modulations at various temporal frequencies (0.25–8 Hz) by using drifting gratings within long or short spatial windows that make the tracking of grating easier or more difficult respectively. Results showed that modulation sensitivity is lowpass for gratings with long windows but bandpass for gratings with short windows (peak at ~1 Hz). Moreover, we found that lowpass sensitivity becomes bandpass when we removed observer attention by a concurrent letter identification task. An additional visual-search experiment showed that a target dot moving with a velocity modulation at relatively high temporal frequencies (~2–4 Hz) was most easily detected among dots moving at various constant velocities. These results support the notion that high sensitivity to sluggish velocity modulation is a product of attentively tracking of moving stimuli and that the visual system is directly sensitive to accelerations and/or decelerations at the preattentive level

Estimated parameters of the MTF for single- and dual-task conditions.

<p>(a) Overall amplitude. (b) Transient factors. (c) Cut-off temporal frequency in hertz. Error bars are +−1 s.e.m. across observers.</p