Two-interval Forced-choice Procedure Research Articles

Exploring quantitative measures in metacognition of emotion

Metacognition of emotion (meta-emotion) refers to the ability to evaluate and identify one’s emotional feelings. No previous study has defined and measured this construct through objective and quantitative procedures. We established a reliable method to measure meta-emotion. With a two-interval forced-choice procedure, participants selected which of two pictures elicited stronger positive emotion; via the Law of Comparative Judgment, their responses were used to compute individual psychological distances for the emotional responses triggered by the pictures. Then, participants were asked to judge whether a pre-exposed picture induced a stronger positive emotion than the median of that elicited by the whole picture set, followed by a confidence rating. By utilizing each individual’s psychological distance, the correctness of a participant’s emotional experience was quantified by dʹ, and meta-emotion was quantified using meta-dʹ, M-ratio, and M-diff as indices of metacognitive sensitivity and efficiency based on Signal-Detection Theory. Test–retest reliabilities, validated by Spearman correlation, were observed in meta-dʹ, M-ratio, and marginally with M-diff, suggesting the stability of meta-emotion in the current design. This study unveils a validated procedure to quantify meta-emotion, extendable for assessing metacognition of other subjective feelings. Nevertheless, caution is warranted in interpretation, as the measured processes may be influenced by non-metacognitive factors.

Measuring the spatial Acuity of vibrotactile Stimuli: A new Approach to determine universal and individual Thresholds

Tactile perception is an increasingly popular gateway in human–machine interaction, yet universal design guidelines for tactile displays are still lacking, largely due to the absence of methods to measure sensibility across skin areas. In this study, we address this gap by developing and evaluating two fully automated vibrotactile tasks that require subjects to discriminate the position of vibrotactile stimuli using a two-interval forced-choice procedure (2IFC). Of the two methodologies, one was initially validated through a preliminary study involving 13 participants. Subsequently, we applied the validated and improved vibrotactile testing procedure to a larger sample of 23 participants, enabling a direct and valid comparison with static stimuli perception. Our findings reveal a significantly finer spatial acuity for static stimuli perception compared to vibrotactile stimuli perception from a stimulus separation of 15mm onwards. This study introduces a novel method for generating both universal thresholds and individual person-specific data for vibratory perception, marking a critical step towards the development of functional vibrotactile displays. The results underline the need for further research in this area and provide a foundation for the development of universal design guidelines for tactile displays.

The effect of blue light filtering lenses on speed perception

Blue-light filtering lenses (BFLs) are marketed to protect the eyes from blue light that may be hazardous to the visual system. Because BFLs attenuate light, they reduce object contrast, which may impact visual behaviours such as the perception of object speed which reduces with contrast. In the present study, we investigated whether speed perception is affected by BFLs. Using a two-interval forced-choice procedure in conjunction with Method of Constant Stimuli, participants (n = 20) judged whether the perceived speed of a moving test stimulus (1.5–4.5°/s) viewed through a BFL was faster than a reference stimulus (2.75°/s) viewed through a clear lens. This procedure was repeated for 3 different BFL brands and chromatic and achromatic stimuli. Psychometric function fits provided an estimate of the speed at which both test and reference stimuli were matched. We find that the perceived speed of both chromatic and achromatic test stimuli was reduced by 6 to 20% when viewed through BFLs, and lenses that attenuated the most blue-light produced the largest reductions in perceived speed. Our findings indicate that BFLs whilst may reduce exposure to hazardous blue light, have unintended consequences to important visual behaviours such as motion perception.

Difference Thresholds for the Perception of Sinusoidal Vertical Stimuli of Whole-Body Vibrations in Ranges of Amplitude and Frequency Relevant to Ride Comfort

Minor differences in the vibration characteristics of a vehicle may greatly influence the comfort experienced by the driver. Therefore, such characteristics are significant in the process of vehicle development. In this experimental study, just-noticeable differences were determined for sinusoidal vertical whole-body vibrations at the frequencies 1.3 Hz and 6.0 Hz, and for the vibration amplitudes 0.2 m/s², 0.5 m/s² and 1.2 m/s². The stimulation set up was realised using a test rig constituting a seating position similar to that in a real vehicle environment. A transformed one-up-three-down method, in conjunction with a two-interval forced choice procedure, was used to determine difference thresholds, in accordance with Weber’s Law, for 14 test subjects. Median relative difference thresholds in the range of 6.7% to 11.0% were observed, and were examined for statistical significance (α < 0.05) and practical importance on amplitude and frequency, with respect to this law. The results showed a frequency-dependence at the lowest vibration amplitude and an amplitude-dependence for both frequencies from a statistical point of view. However, the amplitude-dependence at 6.0 Hz was considered as negligible for practical use.

Vision with different presbyopia corrections simulated with a portable binocular visual simulator.

Presbyopes can choose today among different corrections to provide them with functional vision at far and near, and the outcomes and patient satisfaction depend on the selection. In this study, we present a binocular and portable vision simulator, based on temporal multiplexing of two synchronized tunable lenses allowing see-through and programmable visual simulations of presbyopic corrections. Seventeen binocular corrections were tested: 3 Monofocal (Far, Intermediate, Near), 4 Simultaneous Vision (bifocal, trifocal), 2 Monovision (far and near in either eye) and 8 Modified Monovision corrections (Simultaneous vision in one eye, Monofocal in the other eye). Perceived visual quality was assessed through the simulated corrections in 8 cyclopleged subjects who viewed a composite realistic visual scene with high contrast letters and a landscape at far (4 m) and a high contrast text at intermediate (66 cm) and near (33 cm) distances. Perceptual scores were obtained on a scale of 0 to 5 (low to high perceived quality). Perceptual preference was assessed by judging 36 random image pairs (6 repetitions) viewed through 9 binocular presbyopic corrections using two-interval forced choice procedures. The average score, across far and near distances, was the highest for Monovision (4.4±0.3), followed by Modified Monovision (3.4±0.1), Simultaneous Vision (3.0±0.1) and Monofocal corrections (2.9±0.2). However, the mean difference between far and near was lower for Simultaneous Vision and Monovision (0.4±0.1 PS) than Modified Monovision (1.8±0.7) or monofocal corrections (3.3±1.5). A strong significant correlation was found between the perceptual scores and the percentages of energy in focus, for each correction and distance (R = 0.64, p<0.0001). Multivariate ANOVA revealed significant influence of observation distances (p<10–9) and patients (p = 0.01) on Perceptual Score. In conclusion, we have developed a binocular portable vision simulator that can simulate rapidly and non-invasively different combinations of presbyopic corrections. This tool has applications in systematic clinical evaluation of presbyopia corrections.

Spatiotemporal and Luminance Contrast Properties of Symmetry Perception

Recent studies have shown that limiting the lifetime of pattern elements improves symmetry detection, potentially by increasing the number of element locations. Here, we investigate how spatial relocation, luminance contrast modulation and lifetime duration of elements affect symmetry perception in dynamic stimuli. Stimuli were dynamic dot-patterns containing varying amounts of symmetry about a vertical axis. Symmetrical matched-pairs were: (i) relocated to multiple successive, but random locations (i.e., multiple locations condition); (ii) relocated between the same two locations (i.e., two locations condition); (iii) not, relocated, but their luminance contrast was modulated at different temporal frequencies (i.e., one location condition), and (iv) not relocated, but a single pattern was presented at full contrast (i.e., static condition). In the dynamic conditions, we varied the elements’ lifetime duration and temporal frequency of contrast modulation. We measured symmetry detection thresholds using a two-interval forced choice procedure. Our results show improved performance for the multiple locations condition compared to two-location and static conditions, suggesting a cumulative process whereby weak symmetry information is integrated by spatiotemporal filters to increase overall symmetry signal strength. Performance also improved for the static, contrast modulated patterns, but this was explained by a reduction in perceived density. This suggests that different mechanisms mediate symmetry detection in dynamic stimuli and static contrast modulated patterns.

The Role of Efferent Reduction of Cochlear Compression in the Detection of Tones in Noise

Stimulation of medial olivocochlear (MOC) efferent neurons reduces basilar membrane (BM) sensitivity and increases the slope of BM input-output (I/O) functions in animal models. Decreased compression of I/O functions associated with activation of MOC efferent neurons may assist in extending the neural response to the tone above that of noise, leading to an improvement in masked thresholds. To evaluate this hypothesis, the distortion-product otoacoustic emission (DPOAE) I/O function, a proxy measure of BM compression, was examined in conditions with presentation of contralateral noise. DPOAE I/O functions were measured at f2 frequencies of 1000 and 2000 Hz in 16 normal-hearing adults. In each subject, estimation of masked thresholds at 1000 and 2000 Hz was provided by a two-interval forced-choice procedure. There were statistically significant associations between DPOAE I/O function slopes and masked tone thresholds at both 1000 and 2000 Hz. At 1000 Hz, individuals with higher DPOAE I/O function slopes exhibited lower masked thresholds. Data at 2000 Hz indicated that individuals with higher masked thresholds exhibited higher DPOAE I/O function slopes. When measured with contralateral noise, DPOAE I/O function slopes were linked to masked thresholds at both frequencies examined in this study. Linearized DPOAE I/O functions presumably reflect linearized BM growth functions under conditions of MOC efferent activation, and this process may have extended the neural response to the signal tone so that it could be more easily heard in the presence of masking noise under certain conditions examined in this study.

Older age results in difficulties separating auditory and visual signals in time.

Previous research provides conflicting evidence regarding whether older adults have altered tolerance to timing differences between auditory and visual events. We examine the potential impact of age-related unisensory decline on audiovisual synchrony perception. Fifteen younger (21-32 years) and 13 older (60-72 years) adults participated. To assess unisensory sensitivity, visual Gabor contrast detection thresholds and auditory masked tone pip detection thresholds were measured. Four multisensory conditions were then tested: suprathreshold and near-threshold stimuli (based on individual unisensory psychometric functions), each tested with a masked tone pip stimuli at 0.5 and 4 kHz sound frequencies. Two audiovisual pairs (one synchronous, the other asynchronous) were presented in a two-interval forced-choice procedure, with observers identifying the interval containing the asynchronous stimulus. Older adults required a larger physical asynchrony to perceive the stimuli as asynchronous, particularly for low frequency sounds. Our results demonstrate that the impact of age on audiovisual synchrony perception cannot be explained by decline in unisensory sensitivity alone.

Detection and Discrimination of Motion-Defined Form: Implications for the Use of Night Vision Devices

Superimposed luminance noise is typical of imagery from devices used for low-light vision such as image intensifiers (i.e., night vision devices). In four experiments, we measured the ability to detect and discriminate motion-defined forms as a function of stimulus signal-to-noise ratio at a variety of stimulus speeds. For each trial, observers were shown a pair of image sequences - one containing dots in a central motion-defined target region that moves coherently against the surrounding dots, which moved in the opposite or in random directions, while the other sequence had the same random/uniform motion in both the center and surrounding parts. They indicated which interval contained the target stimulus in a two-interval forced-choice procedure. In the first experiment, simulated night vision images were presented with Poisson-distributed spatiotemporal image noise added to both the target and surrounding regions of the display. As the power of spatiotemporal noise was increased, it became harder for observers to detect the target, particularly at the lowest and highest dot speeds. The second experiment confirmed that these effects also occurred with low illumination in real night vision device imagery, a situation that produces similar image noise. The third experiment demonstrated that these effects generalized to Gaussian noise distributions and noise created by spatiotemporal decorrelation. In the fourth experiment, we found similar speed-dependent effects of luminance noise for the discrimination (as opposed to detection) of the shape of a motion-defined form. The results are discussed in terms of physiological motion processing and for the usability of enhanced vision displays under noisy conditions.

Psychophysical Measures of Sensitivity to Facial Expression of Emotion

We report the development of two simple, objective, psychophysical measures of the ability to discriminate facial expressions of emotion that vary in intensity from a neutral facial expression and to discriminate between varying intensities of emotional facial expression. The stimuli were created by morphing photographs of models expressing four basic emotions, anger, disgust, happiness, and sadness with neutral expressions. Psychometric functions were obtained for 15 healthy young adults using the Method of Constant Stimuli with a two-interval forced-choice procedure. Individual data points were fitted by Quick functions for each task and each emotion, allowing estimates of absolute thresholds and slopes. The tasks give objective and sensitive measures of the basic perceptual abilities required for perceiving and interpreting emotional facial expressions.

Theory and data for area summation of contrast with and without uncertainty: Evidence for a noisy energy model

Contrast sensitivity improves with the area of a sine-wave grating, but why? Here we assess this phenomenon against contemporary models involving spatial summation, probability summation, uncertainty, and stochastic noise. Using a two-interval forced-choice procedure we measured contrast sensitivity for circular patches of sine-wave gratings with various diameters that were blocked or interleaved across trials to produce low and high extrinsic uncertainty, respectively. Summation curves were steep initially, becoming shallower thereafter. For the smaller stimuli, sensitivity was slightly worse for the interleaved design than for the blocked design. Neither area nor blocking affected the slope of the psychometric function. We derived model predictions for noisy mechanisms and extrinsic uncertainty that was either low or high. The contrast transducer was either linear (c(1.0)) or nonlinear (c(2.0)), and pooling was either linear or a MAX operation. There was either no intrinsic uncertainty, or it was fixed or proportional to stimulus size. Of these 10 canonical models, only the nonlinear transducer with linear pooling (the noisy energy model) described the main forms of the data for both experimental designs. We also show how a cross-correlator can be modified to fit our results and provide a contemporary presentation of the relation between summation and the slope of the psychometric function.

Region-based texture segregation and orientation-similarity grouping

Texture segregation and perceptual grouping go hand in hand but they have mostly been studied in separation, each using their own stimuli and tasks, in order to test specific models. For instance, models of texture segregation can be classified as region-based and edge-based, while in perceptual grouping two traditions of models are related to two stimulus types, with elements in random positions (e.g., in snake detection displays) or organized in a grid (e.g., dot lattices). The goal of this study was to provide a more integrated approach. We conducted two psychophysical experiments in which we presented stimuli consisting of oriented Gabors. Perceptual grouping of elements sharing similar orientations may lead to segregation from an ungrouped region with random orientations, or the two regions may be segregated based on local orientation differences at the edge between the regions. We manipulated (1) the degree of orientation similarity in one region by adding orientation jitter to the average orientation (0°–80° in 10° steps), (2) the positions of the Gabors, which were either quasi-random or in a regular grid, and (3) the edge between the two regions, which was either straight or curved. In Experiment 1 a two-interval forced-choice procedure was used with one interval containing only Gabors with random orientations and the other with one region consisting of Gabors in non-random orientations. This experiment required detection of the pattern with a non-random region. Experiment 2 required shape discrimination of the edge (straight or curved) in a yes/no task. We found (1) a gradual decline in performance with increasing orientation jitter in all conditions, (2) lower thresholds for detection of the region than discrimination of the edge, and (3) comparable performance levels for regular and quasi-random Gabor positions. These results are congruent with region-based texture segregation and perceptual grouping.

Human perception of image speed derived from the simultaneous extraction and analysis of visual information in two- and three-dimensional space

An important task of the visual system is to extract speed estimates from the two-dimensional image plane (2D) and from motion in depth (3D), or, as in the majority of scenes, from a combination of both. However, it remains unclear from available research how 2D and 3D speeds are combined. We addressed this issue using a square (5×5deg) Global Dot Motion (GDM) stimulus consisting of 100 circular dots (radius: 8minarc, 90 cd/m2) undergoing random motion on a grey computer screen (45cd/m2). Concurrently, the entire GDM stimulus was displaced in depth (by systematically changing binocular disparity) towards the observer. Using this stimulus, we determined how the 3D speed of the dot-defined square is affected by systematic manipulation of 2D dot speed. A two-interval forced-choice procedure was used. One interval presented the reference stimulus: a dot defined square moving in depth at speeds of 4, 6 and 9cm/sec with no 2D motion, while the other presented the test stimulus: an identical dot defined square, but containing dots moving randomly at speeds of: 0 0.4, 0.8, 1.6 and 3.2cm/sec on the image plane. The task of the observer was to adjust the test stimulus 3D speed to match the reference stimulus. Results show that increasing 2D speed increased the apparent 3D speed of the dot-defined square in a manner consistent with the vector sum of 2D and 3D velocities. We discuss our findings in light of the functional properties of global motion detectors tuned for speed information.

Apparent motion during saccadic suppression periods

Sensitivity to many visual stimuli, and, in particular, image displacement, is reduced during a change in fixation (saccade) compared to when the eye is still. In these experiments, we studied the sensitivity of observers to ecologically relevant image translations of large, complex, real world scenes either during horizontal saccades or during fixation. In the first experiment, we found that such displacements were much less detectable during saccades than during fixation. Qualitatively, even when trans-saccadic scene changes were detectable, they were less salient and appeared slower than equivalent changes in the absence of a saccade. Two further experiments followed up on this observation and estimated the perceived magnitude of trans-saccadic apparent motion using a two-interval forced-choice procedure (Experiment 2) and a magnitude estimation procedure (Experiment 3). Both experiments suggest that trans-saccadic displacements were perceived as smaller than equivalent inter-saccadic displacements. We conclude that during saccades, the magnitude of the apparent motion signal is attenuated as well as its detectability.

Bias and sensitivity in two-interval forced choice procedures: Tests of the difference model

We assess four common claims concerning the two-interval forced choice (2-IFC) procedure and the standard Difference Model of 2-IFC performance. The first two are (1) that it is unbiased and (2) that the structure of the 2-IFC task does not in itself alter sensitivity. The remaining two concern a claimed 2 enhancement in sensitivity in 2-IFC relative to that measured in a Yes–No task. We review relevant past research and re-analyze seventeen experiments from previous studies across three laboratories. We then report an experiment comparing 2-IFC performance with performance in a second task designed to elucidate observers’ decision processes. This second task is simply two successive Yes–No signal detection tasks with the same timing as in the 2-IFC experiment. We find little evidence supporting the claims that 2-IFC is unbiased and that it does not alter sensitivity and we also reject the two claims associated with the Difference Model as a model of performance in our own experiment.

Simultaneous and Independent Acquisition of Multisensory and Unisensory Associations

Although humans are almost constantly exposed to stimuli from multiple sensory modalities during daily life, the processes by which we learn to integrate information from multiple senses to acquire knowledge of multisensory objects are not well understood. Here, we present results of a novel audio-visual statistical learning procedure where participants are passively exposed to a rapid serial presentation of arbitrary audio-visual pairings (comprised of artificial/ synthetic audio and visual stimuli). Following this exposure, participants were tested with a two-interval forced-choice procedure in which their degree of familiarity with the experienced audio-visual pairings was evaluated against novel audio-visual combinations drawn from the same stimulus set. Our results show that subjects acquire knowledge of visual-visual, audio-audio, and audio-visual stimulus associations and that the learning of these types of associations occurs in an independent manner.

Enhanced Optic Flow Speed Discrimination While Walking: Contextual Tuning of Visual Coding

We tested the hypothesis that long-term adaptation to the normal contingencies between walking and its multisensory consequences (including optic flow) leads to enhanced discrimination of appropriate visual speeds during self-motion. In experiments 1 (task 1) and 2 a two-interval forced-choice procedure was used to compare the perceived speed of a simulated visual flow field viewed while walking with the perceived speed of a flow field viewed while standing. Both experiments demonstrated subtractive reductions in apparent speed. In experiments 1 and 3 discrimination thresholds were measured for optic flow speed while walking and while standing. Consistent with the optimal-coding hypothesis, speed discrimination for visual speeds near walking speed was enhanced during walking. Reduced sensitivity was found for slower visual speeds. The multisensory context of walking alters the coding of optic flow in a way that enhances speed discrimination in the expected range of flow speeds.

Neural Mechanisms of the Time-order Error: An MEG Study

The time-order error (TOE) refers to the influence of presentation order on performance accuracy in a discrimination task. Despite it being a well-documented perceptual bias, the underlying mechanisms have not been studied. In this study, observers were trained on a two-interval forced-choice procedure. The stimuli presented for discrimination were a standard, consisting of four tones presented at a 5-Hz rate, and targets, consisting of various rates higher than 5 Hz. Psychometric functions were measured for discrimination of the trained standard and targets, a novel standard of 13 Hz with higher target rates; and the trained 5 Hz standard with novel targets with rates below 5 Hz. Discrimination did not improve with training; in fact, accuracy declined when standard was presented in the first interval during the session, resulting in a TOE. The TOE was specific to the 5-Hz standard generalizing to the novel targets slower than 5 Hz, but not to the 13-Hz STANDARD. Analysis of the event-related magnetic field responses (ERFs) revealed a waveform to the whole stimulus, rather than to each tone in the train. Although ERFs in the second interval were attenuated independent of stimulus type, the M300 component in the second interval was attenuated only when the standard was first, but remained of equivalent magnitude when the standard was second. This was observed only in the two 5-Hz conditions. Combined, these results suggest that the TOE reflects the emergence of an internal representation of the standard, and that the M300 is potentially a neural correlate of plasticity.

Responses to Lightness Variations in Early Human Visual Cortex

Lightness is the apparent reflectance of a surface, and it depends not only on the actual luminance of the surface but also on the context in which the surface is viewed [1-10]. The cortical mechanisms of lightness processing are largely unknown, and the role of early cortical areas is still a matter of debate [11-17]. We studied the cortical responses to lightness variations in early stages of the human visual system with functional magnetic resonance imaging (fMRI) while observers were performing a demanding fixation task. The set of dynamically presented visual stimuli included the rectangular version of the classic Craik-O'Brien stimulus [3, 18, 19] and a variant that led to a weaker lightness effect, as well as a pattern with actual luminance variations. We found that the cortical activity in retinotopic areas, including the primary visual cortex (V1), is correlated with context-dependent lightness variations.

Influence of musical and psychoacoustical training on pitch discrimination

This study compared the influence of musical and psychoacoustical training on auditory pitch discrimination abilities. In a first experiment, pitch discrimination thresholds for pure and complex tones were measured in 30 classical musicians and 30 non-musicians, none of whom had prior psychoacoustical training. The non-musicians’ mean thresholds were more than six times larger than those of the classical musicians initially, and still about four times larger after 2 h of training using an adaptive two-interval forced-choice procedure; this difference is two to three times larger than suggested by previous studies. The musicians’ thresholds were close to those measured in earlier psychoacoustical studies using highly trained listeners, and showed little improvement with training; this suggests that classical musical training can lead to optimal or nearly optimal pitch discrimination performance. A second experiment was performed to determine how much additional training was required for the non-musicians to obtain thresholds as low as those of the classical musicians from experiment 1. Eight new non-musicians with no prior training practiced the frequency discrimination task for a total of 14 h. It took between 4 and 8 h of training for their thresholds to become as small as those measured in the classical musicians from experiment 1. These findings supplement and qualify earlier data in the literature regarding the respective influence of musical and psychoacoustical training on pitch discrimination performance.