Biomedical subjects

Liqiang Huang

Publications and source records attributed to Liqiang Huang.

10 recordsLinked to original sources

PubMed2006

Role of a circle's center in visual interpolation.

Basic geometric patterns like straight lines and circles seem fundamental to human perception and mental imagery. In this study we examined subjects' ability to interpolate circular curves-to derive the whole circle from an arc of 180 degrees or less. Specifically, we tested how the center point is utilized during such visual interpolation. Naturally, a mechanism that interpolates by extending the curvature of the visible arc will be unaffected by the presence or absence of the center point. On the other hand, a mechanism that achieves the same end by completing the circle from estimates of the center and radius will be significantly aided by the presence of the center. We found that when the visible arc was long (180 degrees), presenting the circle's center did not affect the precision with which subjects localized the invisible section. However, when the visible arc was relatively short (90 degrees or 45 degrees), displaying the center point significantly increased spatial precision. Thus, both computational mechanisms appear to exist.

Adult↗

PubMed2006

Contextual cuing based on spatial arrangement of color.

Previous studies have demonstrated that, in visual search, repetition of a target's "context" significantly improves search performance (contextual cuing; Chun & Jiang, 1998). Context in those studies was defined as either spatial configuration or featural combination. In the present work, we demonstrate that repeating the spatial arrangement of object colors (conjunction of spatial configuration and featural combination) also leads to contextual cuing (Experiment 1). Experiments 2 and 3 rule out the possibility that the contextual cuing we find in Experiment 1 is caused only by the spatial configuration of color patches. Experiment 4 rules out the possibility that it is caused only by featural combination. Experiments 5 and 6 demonstrate that color-arrangement-based contextual cuing is an unconscious process. Experiments 7 and 8 demonstrate that contextual cuing seems to be more effective onchromatic (hue) variation than on achromatic (luminance) variation. In sum, our results demonstrate that contextual cuing is not merely associated learning in separate domains; it is a more integrated process than has perhaps been appreciated.

Adolescent↗

PubMed2005

Attention capacity and task difficulty in visual search.

When a visual search task is very difficult (as when a small feature difference defines the target), even detection of a unique element may be substantially slowed by increases in display set size. This has been attributed to the influence of attentional capacity limits. We examined the influence of attentional capacity limits on three kinds of search task: difficult feature search (with a subtle featural difference), difficult conjunction search, and spatial-configuration search. In all 3 tasks, each trial contained sixteen items, divided into two eight-item sets. The two sets were presented either successively or simultaneously. Comparison of accuracy in successive versus simultaneous presentations revealed that attentional capacity limitations are present only in the case of spatial-configuration search. While the other two types of task were inefficient (as reflected in steep search slopes), no capacity limitations were evident. We conclude that the difficulty of a visual search task affects search efficiency but does not necessarily introduce attentional capacity limits.

Attention↗

PubMed2005

Quantifying object salience by equating distractor effects.

It is commonly believed that objects viewed in certain contexts may be more or less salient. Measurements of salience have usually relied on asking observers "How much does this object stand out against the background?". In this study, we measured the salience of objects by assessing the distraction they produce for subjects searching for a different, pre-specified target. Distraction was measured through response times, but changes in response times were not assumed to be a linear measure of distracting potency. The analysis rested on measuring the effects of varying disparities--in size, luminance, and both-between a target object, a key distractor, and other background items. Our results indicate: (1) object salience defined by luminance or size disparity is determined by the ratio between its defining feature value and the corresponding feature value of background items; this finding is congenial to Weber's law for discrimination thresholds. (2) If we define salience as the logarithm of a feature value ratio, then salience increases approximately as fast due to increase in area as due to increase in luminance. (3) The sum of salience arising from object-background disparity in both size and luminance is larger than their vector sum (orthogonal vectors), but smaller than their scalar sum.

Attention↗

PubMed2005

Expectation and repetition effects in searching for featural singletons in very brief displays.

We studied the effects of expectation and repetition on searching for singletons in very brief displays. In Experiment 1, we found that when a given feature defined the singleton for a whole block--so that in every trial the subject could expect a particular target feature--search accuracy was significantly higher than when the feature setting was randomly redetermined from trial to trial. However, an unexpected repetition triggered almost no advantage. In Experiment 2, we found no advantage for expected alternation. Experiments 3 and 4 demonstrated that there is little or no advantage for perception in conditions allowing only for target-feature facilitation or distractor-feature inhibition. We propose that in singleton search a division of feature space facilitates detection, and that this division works best under conditions of expected repetition. Experiment 5 replicated Experiment 1, but in Experiment 5 we examined response times and long display exposures. Results suggested that previous findings of singleton priming reflect mainly postperceptual factors.

Attention↗

PubMed2004

Attentional effects on contrast discrimination in humans: evidence for both contrast gain and response gain.

In order to understand how attention affects visual processing, we investigated the degree to which attention effects can be accounted for by increases in the contrast gain of the contrast response function, CRF (represented by an increase in effective contrast) vs. increases in the response gain (represented by an overall amplification of response). To this end, we used a dual-task paradigm to compare psychophysical "threshold vs. pedestal contrast" (TvC) curves obtained under conditions of full- vs. poor-attention. The attention effect, defined as the ratio of thresholds for poor- vs. full-attention conditions, was roughly four-fold at a pedestal contrast of 0% (i.e., at detection threshold) and there was a significant decrease in attention effect with increasing pedestal contrast, from approximately ten-fold at the lowest non-zero pedestal contrast tested (0.25%) to three-fold at the highest pedestal contrast tested (64%). These findings are consistent with the existence of both contrast gain effects of attention (needed to account for the substantial attention effect at detection threshold and the decrease in attention effect with increasing pedestal contrast) as well as response gain effects of attention (needed to account for the fact that attention was beneficial across all pedestal contrasts-rather than harmful at some contrasts, as a pure contrast gain model would predict). The results of a model fitting Naka-Rushton CRF equations to the TvC data also support this conclusion. Here we found a two-fold increase in contrast gain and a five-fold increase in response gain in the CRF for the full-attention, as compared to the poor-attention, condition. Because pure contrast gain effects, on the order of two-fold, have been observed at early stages of visual processing (for example in areas V4 and MT), our psychophysical results suggest a hybrid model of attention; contrast gain control at an early stage of visual processing, followed by response gain control at a later stage.

Attention↗

PubMed2004

Is contrast just another feature for visual selective attention?

The biased-competition theory of attention [Annual Review of Neuroscience 18 (1995) 193] suggests that attention and stimulus contrast trade off, and implies that high-contrast stimuli should be easy to attend to and hard to ignore. To test this, observers searched displays for a target digit. Observers were well able to exclude high-contrast distractors when attempting to search only among low-contrast stimuli (Experiment 1). In Experiments 2 and 3, location determined which stimuli were relevant. When contrast of relevant and irrelevant stimuli was uncertain (due to contrast varying between trials, Experiment 2), increasing the contrast of distractors impaired performance. However, when contrast was certain (due to blocking of trials, Experiment 3) and targets were of low contrast, high contrast distractors produced less interference than low contrast distractors. The ability of subjects to attend selectively to low vs. high contrast items in Experiments 1 and 3 suggests that selectivity for stimulus contrast might be similar to other types of feature selectivity (e.g., color and location). Such findings are inconsistent with the biased competition theory regarding the interplay of contrast and attention. However, results from Experiment 2 suggest that, when target contrast varies, the default tendency is to attend to high-contrast items.

Adaptation, Physiological↗

PubMed2004

Repetition priming in visual search: episodic retrieval, not feature priming.

Previous research has shown that when the targets of successive visual searches have features in common, response times are shorter. However, the nature of the representation underlying this priming and how priming is affected by the task remain uncertain. In four experiments, subjects searched for an odd-sized target and reported its orientation. The color of the items was irrelevant to the task. When target size was repeated from the previous trial, repetition of target color speeded the response. However, when target size was different from that in the previous trial, repetition of target color slowed responses, rather than speeding them. Our results suggest that these priming phenomena reflect the same automatic mechanism as the priming of pop-out reported by Maljkovic and Nakayama (1994). However, the crossover interaction between repetition of one feature and another rules out Maljkovic and Nakayama's (1994) theory of independent potentiation of distinct feature representations. Instead, we suggest that the priming pattern results from contact with an episodic memory representation of the previous trial.

Association Learning↗

PubMed2004

Are there capacity limitations in symmetry perception?

Previous researchers have proposed that there are two types of symmetry detection: one based on crude preattentive symmetry judgments and another based on detailed scrutiny of individual parts (Barlow & Reeves, 1979; S. E. Palmer & Hemenway, 1978; Royer, 1981). Four experiments were conducted to examine capacity limits in different symmetry judgments. Observers were required to discriminate between random patterns and approximate symmetry (Experiments 1 and 3) or between perfect and approximate symmetry (Experiments 2 and 4). The patterns were divided into two sets of dots, presented either simultaneously or successively. A comparison of accuracy under these two presentation conditions suggested that symmetry detection involves an analysis that is spatially parallel but coarse, regardless of either task difficulty or task type (detecting symmetry vs. detecting asymmetry).

Humans↗

PubMed2002

Symmetry detection and visual attention: a "binary-map" hypothesis.

Recent research suggests that human symmetry-detection mechanisms cannot simultaneously compare different colors across the axis of symmetry (Nature 399 (1999) 115). In the present study, observers were required to judge symmetry in arrays composed of elements varying not only in color, but also in size, spatial frequency and orientation. In every case, response times increased with the number of different levels of a given feature. It is proposed that this increase reflects a sequential strategy whereby coarse "binary maps" are created by attentional filtering, and the symmetry of each map is then checked. Experiment 2 required observers to detect "pseudo-symmetry" (symmetry in feature values defined relative to an arbitrary featural boundary); the ease with which this task was accomplished supported the binary map hypothesis. The results suggest that (1) symmetry detection is spatially imprecise, and (2) attentional gating can operate prior to symmetry detection in the visual pathway.

Adult↗