Biomedical subjects

Chang Hong Liu

Publications and source records attributed to Chang Hong Liu.

5 recordsLinked to original sources

PubMed2003

Differential binocular input and local stereopsis.

Using fractal noise images, we measured the dependence of Dmin and Dmax for stereo on the interocular differences of spatial frequency and contrast. Dmin exhibits a strong dependence on the highest spatial frequency contained in the image, while Dmax exhibits a weaker dependence on the lowest spatial frequency contained within the image. Neither relationship was found to be different when the filtering was restricted to only one eye's image, although the effect of differential lowpass filtering for Dmin was greater than that of binocular lowpass filtering. Contrast is thought to affect stereo performance particularly when it is reduced in only one eye's image. We show that, at least for broadband fractal images representative of everyday natural images, interocular contrast differences are no more disruptive than binocular ones. These results bear upon the nature of the matching process in stereopsis. The fact that these interocular spatial frequency and contrast manipulations do not selectively degrade stereopsis beyond that expected from a consideration of purely monocular effects is consistent with matching occurring within multiple spatial channels prior to their combination.

Contrast Sensitivity↗

PubMed2003

Face recognition with perspective transformation.

The effect of perspective transformation on transfer of face training was investigated in a yes/no recognition task using face stimuli with 42 degrees, 10 degrees, or no perspective convergence. A strong dependence of recognition performance on the magnitude of perspective transformation was found, with large perspective changes such as from 42 degrees at learning to orthogonal at test producing the strongest impairment and small perspective changes such as from 10 degrees at learning to orthogonal at test the least. In a second experiment, the internal and external features of a face from different perspective convergence were artificially combined to produce identical local features between this composite image and the original but producing an impossible perspective transformation from either. The results of transfer between the composite and untouched images showed face recognition to be strongly affected by local featural similarities and relatively insensitive to global coherence of perspective transformation.

Adult↗

PubMed2003

Face recognition is robust with incongruent image resolution: relationship to security video images.

Identifying a criminal captured on conventional security video typically requires matching poor-quality video footage against a high-quality photograph. The authors examined the consequence of such a large discrepancy in image quality. Recognition and matching performance of this incongruent-quality condition was compared with that of a congruent one, in which a high-quality photograph was reduced to a low-quality video. Recognition memory was little affected by this manipulation, whereas matching performance of the incongruent condition enjoyed occasional advantage. The results show that person identification can tolerate a large discrepancy between image qualities of matching stimuli when one of the images is of poor quality.

Adolescent↗

PubMed2002

Reassessing the 3/4 view effect in face recognition.

It is generally accepted that unfamiliar faces are better recognized if presented in 3/4 view. A common interpretation of this result is that the 3/4 view represents a canonical view for faces. This article presents a critical review of this claim. Two kinds of advantage, in which a 3/4 view either generalizes better to a different view or produces better recognition in the same view, are discussed. Our analysis of the literature shows that the first effect almost invariably depended on different amounts of angular rotation that was present between learning and test views. The advantage usually vanished when angular rotation was equalized between conditions. Reports in favor of the second effect are scant and can be countered by studies reporting negative findings. To clarify this ambiguity, we conducted a recognition experiment. Subjects were trained and tested on the same three views (full-face, 3/4 and profile). The results showed no difference between the three view conditions. Our analysis of the literature, along with the new results, shows that the evidence for a 3/4 view advantage in both categories is weak at best. We suggest that a better predictor of performance for recognition in different views is the angular difference between learning and test views. For recognition in the same view, there may be a wide range of views whose effectiveness is comparable to the 3/4 view.

Adolescent↗

PubMed2002

Luminance spatial scale and local stereo-sensitivity.

Using filtered, broad band, fractal noise images we measured the dependence of D(min) and D(max) for stereo on luminance spatial frequency. D(min) was found to exhibit a simple dependence on the highest spatial frequency contained in the stimulus. D(max) depended on both image size and spatial frequency in a way that suggests an informational limit. Different rules govern D(min) and D(max) even for first order stereopsis, arguing against a common neural explanation based on independent access to the most pertinent spatial filter.

Depth Perception↗