Method Of Single Stimuli Research Articles

BIQ2021: a large-scale blind image quality assessment database

The assessment of the perceptual quality of digital images is becoming increasingly important as a result of the widespread use of digital multimedia devices. Smartphones and high-speed internet are just two examples of technologies that have multiplied the amount of multimedia content available. Thus, obtaining a representative dataset, which is required for objective quality assessment training, is a significant challenge. The Blind Image Quality Assessment Database, BIQ2021, is presented in this article. By selecting images with naturally occurring distortions and reliable labeling, the dataset addresses the challenge of obtaining representative images for no-reference image quality assessment. The dataset consists of three sets of images: those taken without the intention of using them for image quality assessment, those taken with intentionally introduced natural distortions, and those taken from an open-source image-sharing platform. It is attempted to maintain a diverse collection of images from various devices, containing a variety of different types of objects and varying degrees of foreground and background information. To obtain reliable scores, these images are subjectively scored in a laboratory environment using a single stimulus method. The database contains information about subjective scoring, human subject statistics, and the standard deviation of each image. The dataset's Mean Opinion Scores (MOS) make it useful for assessing visual quality. Additionally, the proposed database is used to evaluate existing blind image quality assessment approaches, and the scores are analyzed using Pearson and Spearman's correlation coefficients. The image database and MOS are freely available for use and benchmarking.

Somatotopic representation of tactile duration: evidence from tactile duration aftereffect

Accurate perception of sub-second tactile duration is critical for successful human-machine interaction and human daily life. However, it remains debated where the cortical processing of tactile duration takes place. Previous studies have shown that prolonged adaptation to a relatively long or short auditory or visual stimulus leads to a repulsive duration aftereffect such that the durations of subsequent test stimuli within a certain range appear to be contracted or expanded. Here, we demonstrated a robust repulsive tactile duration aftereffect with the method of single stimuli, where participants determined whether the duration of the test stimulus was shorter or longer than the internal mean formed before the adaptation (Experiment 1A). The tactile duration aftereffect was also observed when participants reproduced the duration of the test stimulus by holding down a button press (Experiment 1B). Importantly, the observed tactile duration aftereffect was tuned around the adapting duration (Experiment 1C). Moreover, the effect was confined in the adapted sensory modality (Experiment 2) and the enacted fingers within a somatotopic framework (Experiment 3). These findings suggest the early somatosensory areas with the topographic organization of hands play an essential role in sub-second tactile duration perception.

Performance of Four Subjective Video Quality Assessment Protocols and Impact of Different Rating Preprocessing and Analysis Methods

Standardization bodies recommend various protocols to conduct subjective quality assessment (QA) of imaging systems. While many studies have compared these QA protocols, few have assessed the impact of different approaches for preprocessing and analyzing quality ratings. Furthermore, the effect of large versus small quality differences on the discrimination performance of protocols has not been extensively studied in video QA. This study examines these issues for four QA protocols. H.264 compressed medical videos and denoised natural scene videos were evaluated by expert and naive subjects. Scores were collected with four QA protocols—forced choice (FC), two ratio-scaled paired comparison methods: preference (Pref) and dissimilarity (Dissim), and single stimulus (SS)—and analyzed using combinations of different rating preprocessing approaches, generating a total of 14 methods. Performance metrics—probability and effect size—quantified the ability of the methods to discriminate between quality levels. The Pref and Dissim methods analyzed with classical multidimensional scaling and the SS method with Z-score transformation consistently outperformed the other methods. The type of preprocessing introduced large differences in the performance of individual protocols. Grouping stimuli pairs by small and large quality differences introduced significant differences in the performance rankings of the methods, with Pref and Dissim being most sensitive to small quality differences. For the future, we suggest further validation of the FC method, due to its simplicity and ease of use, and continued investigation into more robust raw scores transformation and statistical analysis methods for both SS and FC ratings.

The absolute disparity anomaly and the mechanism of relative disparities.

There has been a long-standing debate about the mechanisms underlying the perception of stereoscopic depth and the computation of the relative disparities that it relies on. Relative disparities between visual objects could be computed in two ways: (a) using the difference in the object's absolute disparities (Hypothesis 1) or (b) using relative disparities based on the differences in the monocular separations between objects (Hypothesis 2). To differentiate between these hypotheses, we measured stereoscopic discrimination thresholds for lines with different absolute and relative disparities. Participants were asked to judge the depth of two lines presented at the same distance from the fixation plane (absolute disparity) or the depth between two lines presented at different distances (relative disparity). We used a single stimulus method involving a unique memory component for both conditions, and no extraneous references were available. We also measured vergence noise using Nonius lines. Stereo thresholds were substantially worse for absolute disparities than for relative disparities, and the difference could not be explained by vergence noise. We attribute this difference to an absence of conscious readout of absolute disparities, termed the absolute disparity anomaly. We further show that the pattern of correlations between vergence noise and absolute and relative disparity acuities can be explained jointly by the existence of the absolute disparity anomaly and by the assumption that relative disparity information is computed from absolute disparities (Hypothesis 1).

Aging and visual memory: Modified method of single stimuli reveals biases and imprecision

Aging and visual memory: Modified method of single stimuli reveals biases and imprecision

Aging and visual length discrimination: Sequential dependencies, biases, and the effects of multiple implicit standards

Younger (20-25 years of age) and older (61-79 years) adults were evaluated for their ability to visually discriminate length. Almost all experiments that have utilized the method of single stimuli to date have required participants to judge test stimuli relative to a single implicit standard (for a rare exception, see Morgan, On the scaling of size judgements by orientational cues, Vision Research, 1992, 32, 1433-1445). In the current experiments, we not only asked participants to judge lengths relative to a single implicit standard, but they also compared test stimuli to two different implicit standards within the same blocks of trials. We analyzed our participants' judgments to evaluate whether significant sequential dependencies occurred. We found that while individual younger and older adults possessed similar length difference thresholds and exhibited similar overall biases, the judgments of older adults within individual blocks of trials were more strongly biased (than younger adults) by preceding responses (i.e., their judgments on any given trial were more strongly affected by responses to previously viewed stimuli). In addition, the judgments of both younger and older adults were more strongly biased by preceding responses in the blocks of trials with multiple implicit standards. Overall, our results are consistent with the operation of the tracking mechanism described by Criterion-setting theory (Lages and Treisman, Spatial frequency discrimination: Visual long-term memory or criterion setting? Vision Research, 1998, 38, 557-572).

A bias-free measure of retinotopic tilt adaptation

The traditional method of single stimuli for measuring perceptual illusions and context effects confounds perceptual effects with changes in the observer's decision criterion. By deciding consciously or unconsciously to select one of the two response alternatives more than the other when unsure of the correct response, the observer can shift his or her psychometric function in a manner indistinguishable from a genuine perceptual shift. Here, a spatial two-alternative forced-choice method is described to measure a perceptual aftereffect by its influence on the shape of the psychometric function rather than the mean. The method was tested by measuring the effect of motion adaptation on the apparent Vernier offset of stationary Gabor patterns. The shift due to adaptation was found to be comparable in size to the internal noise, estimated from the slope of the psychometric function. By moving the eyes between adaptation and test, it was determined that adaptation is retinotopic rather than spatiotopic.

Comparison of Event-Related Potential in Opinion Tests of Picture Quality and Preference with Food Pictures

In order to study on event-related potential (ERP) in opinion tests of picture quality and food evaluation, the ERPs were measured at 14 electrode positions by the same evaluation method with the same picture, and the same subjects. The pictures of sushi were used. ERP waveform of opinion tests with stimulus-comparison and single-stimulus methods were compared. In result, the ERP waveform of picture quality test has one peak, and the waveform of food preference test has two peaks. The P300 amplitude in the cases of picture quality and food preference tests with stimulus-comparison method is different at Fz and F7. And there is no significant difference between P300 amplitudes of the cases with stimulus-comparison and single-stimulus methods in food preference test. These results indicate that a difference by evaluation method is small, and the content of the evaluation task such as picture quality or food preference is one of the causes.

Differences in perceptual latency estimated from judgments of temporal order, simultaneity and duration are inconsistent.

Differences in perceptual latency (ΔL) for two stimuli, such as an auditory and a visual stimulus, can be estimated from temporal order judgments (TOJ) and simultaneity judgments (SJ), but previous research has found evidence that ΔL estimated from these tasks do not coincide. Here, using an auditory and a visual stimulus we confirmed this and further show that ΔL as estimated from duration judgments also does not coincide with ΔL estimated from TOJ or SJ. These inconsistencies suggest that each judgment is subject to different processes that bias ΔL in different ways: TOJ might be affected by sensory interactions, a bias associated with the method of single stimuli and an order difficulty bias; SJ by sensory interactions and an asymmetrical criterion bias; duration judgments by an order duration bias.

Linking hypotheses underlying Class A and Class B methods

Class A psychophysical observations are based on the linking hypothesis that perceptually distinguishable stimuli must correspond to different brain events. Class B observations are related to the appearance of stimuli not their discriminability. There is no clear linking hypothesis underlying Class B observations, but they are necessary for studying the effects of context on appearance, including a large class of phenomena known as "illusions." Class B observations are necessarily measures of observer bias (Fechner's "constant error") as opposed to Class A measures of sensitivity (Fechner's "variable error"). It is therefore important that Class B observations distinguish between response biases, decisional biases, and perceptual biases. This review argues that the commonly used method of single stimuli fails to do this, and that multiple-alternative forced choice (mAFC) methods can do a better job, particularly if combined with a roving pedestal.

Shifts of the psychometric function: Distinguishing bias from perceptual effects

Morgan, Dillenburger, Raphael, and Solomon have shown that observers can use different response strategies when unsure of their answer, and, thus, they can voluntarily shift the location of the psychometric function estimated with the method of single stimuli (MSS; sometimes also referred to as the single-interval, two-alternative method). They wondered whether MSS could distinguish response bias from a true perceptual effect that would also shift the location of the psychometric function. We demonstrate theoretically that the inability to distinguish response bias from perceptual effects is an inherent shortcoming of MSS, although a three-response format including also an "undecided" response option may solve the problem under restrictive assumptions whose validity cannot be tested with MSS data. We also show that a proper two-alternative forced-choice (2AFC) task with the three-response format is free of all these problems so that bias and perceptual effects can easily be separated out. The use of a three-response 2AFC format is essential to eliminate a confound (response bias) in studies of perceptual effects and, hence, to eliminate a threat to the internal validity of research in this area.

Observers can voluntarily shift their psychometric functions without losing sensitivity

Psychometric sensory discrimination functions are usually modeled by cumulative Gaussian functions with just two parameters, their central tendency (μ) and their slope (1/σ). These correspond to Fechner’s “constant” and “variable” errors, respectively. Fechner pointed out that even the constant error could vary over space and time and could masquerade as variable error. We wondered whether observers could deliberately introduce a constant error into their performance without loss of precision. In three-dot vernier and bisection tasks with the method of single stimuli, observers were instructed to favour one of the two responses when unsure of their answer. The slope of the resulting psychometric function was not significantly changed, despite a significant change in central tendency. Similar results were obtained when altered feedback was used to induce bias. We inferred that observers can adopt artificial response criteria without any significant increase in criterion fluctuation. These findings have implications for some studies that have measured perceptual “illusions” by shifts in the psychometric functions of sophisticated observers.

Effect of camera separation on the viewing experience of stereoscopic photographs

This study presents a geometric and subjective analysis of typical mobile stereoscopic 3-D images. The geometry of the stereoscopic pipeline from the scene to the eyes of the viewer is a highly relevant issue in stereoscopic media. One important factor is camera separation, because it can be used to control the perceived depth of stereoscopic images. The geometric analysis included consideration of disparity and roundness factor within typical mobile stereoscopic imaging scenes. These geometric properties of stereoscopic 3-D images were compared to subjective evaluations by varying camera separation in different scenes. The participants in this study evaluated the strength and naturalness of depth sensation and the overall viewing experience from still images with the single-stimulus method. The results showed that participants were able to perceive the change of depth range even though the images were shown in random order without a reference depth scale. The highest naturalness of depth sensation and viewing experience were achieved with 2 cm to 6 cm camera separation in every content. With these preferred camera separations, the disparity range was less than ±1 deg⁡ and cardboard effect (quantified with roundness factor) did not negatively affect the naturalness of depth sensation.

Observers can voluntarily shift their psychometric functions without losing sensitivity

Psychometric sensory discrimination functions are usually modeled by cumulative Gaussian functions with just two parameters, their central tendency (μ) and their slope (1/σ). These correspond to Fechner’s “constant” and “variable” errors, respectively. Fechner pointed out that even the constant error could vary over space and time and could masquerade as variable error. We wondered whether observers could deliberately introduce a constant error into their performance without loss of precision. In three-dot vernier and bisection tasks with the method of single stimuli, observers were instructed to favour one of the two responses when unsure of their answer. The slope of the resulting psychometric function was not significantly changed, despite a significant change in central tendency. Similar results were obtained when altered feedback was used to induce bias. We inferred that observers can adopt artificial response criteria without any significant increase in criterion fluctuation. These findings have implications for some studies that have measured perceptual “illusions” by shifts in the psychometric functions of sophisticated observers.

Motion perception and ageing at scotopic light levels

We investigated how elderly observers perceive scotopic motion. Full-screen drifting sinusoidal gratings generated by CRS VSG-2/3 were presented on a 21-inch Sony monitor for 500 ms. Scotopic conditions were simulated using neutral density filters. Following 30 min dark adaptation, motion detection and speed discrimination thresholds were measured in two groups of young (20–30 years) and older (50–75years) subjects. Motion detection threshold was assessed for two spatial frequencies at both ends of the visible range. Grating speed varied starting from a very low value, according to the method of constant stimuli involving forced choice direction discrimination task. Speed discrimination performance for the same spatial frequencies was studied using the method of single stimuli. Subjects indicated if the grating was moving faster or slower than the mean drift rate of the range. Slow (2.6 deg/s) and faster (9.2 deg/s) drift rates were used. Older subjects, unable to detect slow moving gratings, had higher motion detection threshold than younger subjects especially at low spatial frequency. Speed discrimination worsened for older subjects, more so at the low drift rate. Scotopic CSF did not correlate with the loss demonstrated by older subjects. Our results indicate visual motion processing impairments with age under scotopic conditions.

Visual memories for perceived length are well preserved in older adults

Three experiments compared younger (mean age was 23.7 years) and older (mean age was 72.1 years) observers’ ability to visually discriminate line length using both explicit and implicit standard stimuli. In Experiment 1, the method of constant stimuli (with an explicit standard) was used to determine difference thresholds, whereas the method of single stimuli (where the knowledge of the standard length was only implicit and learned from previous test stimuli) was used in Experiments 2 and 3. The study evaluated whether increases in age affect older observers’ ability to learn, retain, and utilize effective implicit visual standards. Overall, the observers’ length difference thresholds were 5.85% of the standard when the method of constant stimuli was used and improved to 4.39% of the standard for the method of single stimuli (a decrease of 25%). Both age groups performed similarly in all conditions. The results demonstrate that older observers retain the ability to create, remember, and utilize effective implicit standards from a series of visual stimuli.

Vision senses number directly

We have recently suggested that numerosity is a primary sensory attribute, and shown that it is strongly susceptible to adaptation. Here we use the Method of Single Stimuli to show that observers can extract a running average of numerosity of a succession of stimuli to use as a standard of comparison for subsequent stimuli. On separate sessions observers judged whether the perceived numerosity or density of a particular trial was greater or less than the average of previous stimuli. Thresholds were as precise for this task as for explicit comparisons of test with standard stimuli. Importantly, we found no evidence that numerosity judgments are mediated by density. Under all conditions, judgements of numerosity were as precise as those of density. Thresholds in intermingled conditions, where numerosity varied unpredictably with density, were as precise as the blocked thresholds. Judgments in constant-density conditions were more precise thresholds than those in variable-density conditions, and numerosity judgements in conditions of constant-numerosity showed no tendency to follow density. We further report the novel finding that perceived numerosity increases with decreasing luminance, whereas texture density does not, further evidence for independent processing of the two attributes. All these measurements suggest that numerosity judgments can be, and are, made independently of judgments of the density of texture.

Vision senses number directly

AbstractWe have recently suggested that numerosity is a primary sensory attribute, showing that it is strongly susceptible to adaptation. Here we use the Method of Single Stimuli (MSS) to show that observers can extract a running average of the numerosity of a succession of stimuli and hold it in mind for use as a standard of comparison for subsequent stimuli. Accuracy and precision of judgments are high and not reduced by potentially misleading variables like texture density or display area.

The Role of Explicit and Implicit Standards in Visual Speed Discrimination

Five experiments were designed to investigate visual speed discrimination. Variations of the method of constant stimuli were used to obtain speed discrimination thresholds in experiments 1, 2, 4, and 5, while the method of single stimuli was used in experiment 3. The observers' thresholds were significantly influenced by the choice of psychophysical method and by changes in the standard speed. The observers' judgments were unaffected, however, by changes in the magnitude of random variations in stimulus duration, reinforcing the conclusions of Lappin et al (1975 Journal of Experimental Psychology: Human Perception and Performance 1 383 394). When an implicit standard was used, the observers produced relatively low discrimination thresholds (7.0% of the standard speed), verifying the results of McKee (1981 Vision Research 21 491-500). When an explicit standard was used in a 2AFC variant of the method of constant stimuli, however, the observers' discrimination thresholds increased by 74% (to 12.2%), resembling the high thresholds obtained by Mandriota et al (1962 Science 138 437-438). A subsequent signal-detection analysis revealed that the observers' actual sensitivities to differences in speed were in fact equivalent for both psychophysical methods. The formation of an implicit standard in the method of single stimuli allows human observers to make judgments of speed that are as precise as those obtained when explicit standards are available.

Attention and the subjective expansion of time

During brief, dangerous events, such as car accidents and robberies, many people report that events seem to pass in slow motion, as if time had slowed down. We have measured a similar, although less dramatic, effect in response to unexpected, nonthreatening events. We attribute the subjective expansion of time to the engagement of attention and its influence on the amount of perceptual information processed. We term the effect time's subjective expansion (TSE) and examine here the objective temporal dynamics of these distortions. When a series of stimuli are shown in succession, the low-probability oddball stimulus in the series tends to last subjectively longer than the high-probability stimulus even when they last the same objective duration. In particular, (1) there is a latency of at least 120 msec between stimulus onset and the onset of TSE, which may be preceded by subjective temporal contraction; (2) there is a peak in TSE at which subjective time is particularly distorted at a latency of 225 msec after stimulus onset; and (3) the temporal dynamics of TSE are approximately the same in the visual and the auditory domains. Two control experiments (in which the methods of magnitude estimation and stimulus reproduction were used) replicated the temporal dynamics of TSE revealed by the method of constant stimuli, although the initial peak was not apparent with these methods. In addition, a third, control experiment (in which the method of single stimuli was used) showed that TSE in the visual domain can occur because of semantic novelty, rather than image novelty per se. Overall, the results support the view that attentional orienting underlies distortions in perceived duration.