Staircase Procedure Research Articles

Simultaneous density contrast and binocular integration

Most research on texture density has utilized textures rendered as two-dimensional (2D) planar surfaces, consistent with the conventional definition of density as the number of texture elements per unit area. How the brain represents texture density information in the three-dimensional (3D) world is not yet clear. Here we tested whether binocular information affects density processing using simultaneous density contrast (SDC), in which the perceived density of a texture region is changed by a surround of different density. We considered the effect on SDC of two types of binocular information: the stereoscopic depth relationships and the interocular relationships between the center and surround textures. Observers compared the perceived density of two random dot patterns, one with a surround (test stimulus) and one without (match), using a 2AFC staircase procedure. In Experiment 1 we manipulated the stereo-depth of the surround plane systematically from near to far, relative to the center plane. SDC was reduced when the difference in stereo-depth between test center and surround increased. In Experiment 2 we spread the surround dots randomly across a stereo-depth volume from small to large volume sizes, and found that SDC was slightly reduced with volume size. The decrease of SDC in both experiments was observed with dense surrounds only, but not with sparse surrounds. In the last experiment we presented center and surround in the same depth plane but dichopticly, monopticly, and binocularly. A strong interocular transfer of SDC was found in the dichoptic condition. Together these results show that texture density processing is sensitive to binocularity.

Adaptation to interocular difference.

Patterns in the two eyes' views that are not identical in hue or contrast often elicit an impression of luster, providing a cue for discriminating them from perfectly matched patterns. Here we ask whether the mechanism for detecting interocular differences (IDs) is adaptable. Our stimuli were horizontally oriented multispatial-frequency grating patterns that could be subject to varying degrees of ID through the introduction of interocular phase differences in the grating components. Subjects adapted to patterns that were either correlated, uncorrelated, monocular (one eye only), or anticorrelated. Following adaptation, thresholds for detecting IDs were measured using a staircase procedure. It was found that ID thresholds were elevated following adaptation to uncorrelated, monocular, and anticorrelated but not correlated patterns. Threshold elevation was found to be maximal when the orientations of the adaptor and test gratings were the same, and when their spatial frequencies were similar. The results support the existence of a specialized mechanism for detecting IDs, the most likely candidate being the binocular differencing channel proposed in previous studies.

Extrafoveally applied flashing light affects contrast thresholds of achromatic and S-cone isolating, but not L-M cone modulated stimuli

Flashing light stimulation is often used to investigate the visual system. However, the magnitude of the effect of this stimulus on the various subcortical pathways is not well investigated. The signals of conscious vision are conveyed by the magnocellular, parvocellular and koniocellular pathways. Parvocellular and koniocellular pathways (or more precisely, the L-M opponent and S-cone isolating channels) can be accessed by isoluminant red-green (L-M) and S-cone isolating stimuli, respectively. The main goal of the present study was to explore how costimulation with strong white extrafoveal light flashes alters the perception of stimuli specific to these pathways. Eleven healthy volunteers with negative neurological and ophthalmological history were enrolled for the study. Isoluminance of L-M and S-cone isolating sine-wave gratings was set individually, using the minimum motion procedure. The contrast thresholds for these stimuli as well as for achromatic gratings were determined by an adaptive staircase procedure where subjects had to indicate the orientation (horizontal, oblique or vertical) of the gratings. Thresholds were then determined again while a strong white peripheral light flash was presented 50 ms before each trial. Peripheral light flashes significantly (p < 0.05) increased the contrast thresholds of the achromatic and S-cone isolating stimuli. The threshold elevation was especially marked in case of the achromatic stimuli. However, the contrast threshold for the L-M stimuli was not significantly influenced by the light flashes. We conclude that extrafoveally applied light flashes influence predominantly the perception of achromatic stimuli.

Self‐assessment of refractive errors using a simple optical approach

BackgroundThis explorative study investigated procedures for the self‐assessment of spherocylindrical refractive errors.MethodsEighteen participants with a mean age of 34.0 ± 8.8-years were enrolled. Adjustable Alvarez lenses were mounted in a rotatable ring holder and two procedures were tested for the self‐adjustment: (1) rotation of the lens in three meridians: 0°, 60° and 120° and (2) rotation of the optotypes in the same meridians. Starting from maximum positive power, the participants were required to decrease the power of the Alvarez lens until the optotypes (0.0 logMAR) appeared to be clear the first time. Best‐corrected visual acuity (BVA) was measured using a psychophysical staircase procedure. Bland–Altmann analysis was carried out in order to calculate the limits of agreement between the self‐refraction method and the standard subjective refraction.ResultsUsing procedure 1, 77-per cent of the subjects achieved a VA ≥ 0.1 logMAR (6/7.5) and the same was true for 88-per cent of the subjects using procedure 2. Using procedure 1, a significantly worse BVA was found, when compared to subjective refraction (ΔVA = −0.15 logMAR, F3,140 = 7.11, p = 0.046, median test). Analysis of variance (ANOVA) analysis showed a significant influence of the refraction method on the oblique astigmatism component J45 but not for the spherical equivalent M and the straight astigmatism component J0 (M: F3,140 = 0.532, p = 0.661; J0: F3,140 = 0.056, p = 0.983; J45: F3,140 = 13.97, p < 0.001; ANOVA). The limits of agreement for the spherical equivalent error M were ± 1.10-D and ± 1.20-D and for the astigmatic components J0 ± 0.78-D and ± 0.59-D and for J45 ± 0.62-D and ± 0.54-D, for procedure 1 and procedure 2, respectively.ConclusionsFixed adjustable Alvarez lenses and rotatable stimuli can provide a fast and precise self‐assessment method to measure the spherocylindrical error of the eye.

An adaptive semantic matching paradigm for reliable and valid language mapping in individuals with aphasia.

Research on neuroplasticity in recovery from aphasia depends on the ability to identify language areas of the brain in individuals with aphasia. However, tasks commonly used to engage language processing in people with aphasia, such as narrative comprehension and picture naming, are limited in terms of reliability (test-retest reproducibility) and validity (identification of language regions, and not other regions). On the other hand, paradigms such as semantic decision that are effective in identifying language regions in people without aphasia can be prohibitively challenging for people with aphasia. This paper describes a new semantic matching paradigm that uses an adaptive staircase procedure to present individuals with stimuli that are challenging yet within their competence, so that language processing can be fully engaged in people with and without language impairments. The feasibility, reliability and validity of the adaptive semantic matching paradigm were investigated in sixteen individuals with chronic post-stroke aphasia and fourteen neurologically normal participants, in comparison to narrative comprehension and picture naming paradigms. All participants succeeded in learning and performing the semantic paradigm. Test-retest reproducibility of the semantic paradigm in people with aphasia was good (Dice coefficient=0.66), and was superior to the other two paradigms. The semantic paradigm revealed known features of typical language organization (lateralization; frontal and temporal regions) more consistently in neurologically normal individuals than the other two paradigms, constituting evidence for validity. In sum, the adaptive semantic matching paradigm is a feasible, reliable and valid method for mapping language regions in people with aphasia.

Aerobic exercises worsen the detection threshold of short H2S pulses

Whether smelling is reduced during aerobic exercise is described contradictorily in the sparse literature. To clarify this question, in healthy subjects the passive detection thresholds for short H2S stimuli were determined by means of a flow olfactometer in an inspiration-synchronous manner during nasal breathing in a staircase procedure during a resting phase, a subsequent submaximal load on a bicycle ergometer and a subsequent recovery phase. In parallel, the measurements of heart rate, blood pressure, blood lactate and body temperature were monitored to confirm an aerobic exercise. The participants achieved the highest values for the detection threshold in the load phase. By means of rm-ANOVA and post-hoc tests, a significant difference in the mean values of detection thresholds between the measurements at rest and during cycling as well as between the recovery and load phases was observed. However, the mean values of the detection thresholds between the resting and recovery phases did not differ. The worsening of olfactory detection thresholds during acute aerobic physical exercise and their immediate improvement during recovery phase to rest values suggests that the detection threshold is influenced by exercise. The most probable cause for this is a dilution effect caused by additional inflowing neutral ambient air in the case of forced nasal breathing.

Effect of eccentricity and light level on the timing of light adaptation mechanisms.

We explored the complexity of the light adaptation process, assessing adaptation recovery (Ar) at different eccentricities and light levels. Luminance thresholds were obtained with transient background fields at mesopic and photopic light levels for temporal retinal eccentricities (0°-15°) with test/background stimulus size of 0.5°/1° using a staircase procedure in a two-channel Maxwellian view optical system. Ar was obtained in comparison with steady data [Vis. Res.125, 12 (2016)VISRAM0042-698910.1016/j.visres.2016.04.008]. Light level proportionally affects Ar only at fovea. Photopic extrafoveal thresholds were one log unit higher for transient conditions. Adaptation was equally fast at low light levels for different retinal locations with variations mainly affected by noise. These results evidence different timing in the mechanisms of adaptation involved.

Age-related changes in ON and OFF responses to luminance increments and decrements.

Impulse response functions for an incremental luminous pulse (ON flash) or a decremental luminous pulse (OFF flash) were derived for twelve young (19-24 years old) and ten old (65-84 years old) observers. Thresholds were measured for two pulses separated by stimulus-onset-asynchronies from 13.3 to 186.7 ms. The pulses had a spatial Gaussian shape and were presented as increments or decrements on a 15 cd/m2 equal-energy white background, having the same chromaticity as the pulse. A spatial four-alternative forced-choice method was combined with a staircase procedure. Retinal illuminance was equated individually by heterochromatic flicker photometry and using a 2.3-mm exit pupil in a Maxwellian-view optical system to reduce the effects of age-related changes and individual variations in lens density and pupil size. Luminance ON- and OFF-impulse response functions calculated from the threshold data revealed significant age-related changes in the response amplitude of both first excitatory and first inhibitory phases. However, there were no significant changes in the time to the first peak or the second peak. These age-related changes in luminance varying ON- and OFF-impulse response functions (IRFs), reflecting putative properties of the magnocellular pathway, are discussed in relation to motion detection and the balance of ON and OFF pathways across the life span.

Fixation distance and fixation duration to vertical road signs

The distance of first-fixation to vertical road signs was assessed in 22 participants while driving a route of 8.34 km. Fixations to road signs were recorded by a mobile eye-movement-tracking device synchronized to GPS and kinematic data. The route included 75 road signs. First-fixation distance and fixation duration distributions were positively skewed. Median distance of first-fixation was 51 m. Median fixation duration was 137 ms with a modal value of 66 ms. First-fixation distance was linearly related to speed and fixation duration. Road signs were gazed at a much closer distance than their visibility distance. In a second study a staircase procedure was used to test the presentation-time threshold that lead to a 75% accuracy in road sign identification. The threshold was 35 ms, showing that short fixations to a road signs could lead to a correct identification.

Exploring the sentence advantage in working memory: Insights from serial recall and recognition

Immediate serial recall of sentences has been shown to be superior to that of unrelated words. This study was designed to further explore how this effect might emerge in recall and to establish whether it also extends to serial recognition, a different form of response task that has relatively reduced output requirements. Using auditory or visual presentation of sequences, we found a substantial advantage for sentences over lists in serial recall, an effect shown on measures of recall accuracy, order, intrusion, and omission errors and reflected in transposition gradients. In contrast however, recognition memory based on a standard change detection paradigm gave only weak and inconsistent evidence for a sentence superiority effect. However, when a more sensitive staircase procedure imported from psychophysics was used, a clear sentence advantage was found although the effect sizes were smaller than those observed in serial recall. These findings suggest that sentence recall benefits from automatic processes that utilise long-term knowledge across encoding, storage, and retrieval.

Symmetric visual response to positive and negative induced spherical defocus under monochromatic light conditions

The purpose of the study was to investigate the sign-dependent response to real and simulated spherical defocus on the visual acuity under monochromatic light conditions. The investigation included 15 myopic participants with a mean spherical equivalent error of −2.98 ± 2.17 D. Visual acuity (VA) was tested with and without spherical defocus using the source method (simulated defocus) and the observer method (lens-induced defocus) in a range of ±3.0 D in 1.0 D steps. VA was assessed using Landolt C’s, while the threshold was determined with an adaptive staircase procedure. Monochromatic light conditions were achieved using band pass filters with a wavelength of 450 ± 2 nm, 530 ± 2 nm and 630 ± 2 nm. Results showed that the reduction of VA was significantly different under blue lighting conditions, when compared to the green and red light conditions. No significant difference in the reduction of the VA was found between the positive and the negative sign of defocus for all lighting conditions. The agreement for the VA between the source and observer method was significantly dependent on the wavelength as well as on the level of defocus. To conclude, under monochromatic light conditions, myopes show a symmetric sign-dependency regarding the influence of spherical defocus on visual acuity. The observed results indicate that the human visual system is capable of integrating the chromatic differences in refraction to distinguish between the signs of defocus.

Perceptual learning of faces: a rehabilitative study of acquired prosopagnosia

Despite many studies of acquired prosopagnosia, there have been only a few attempts at its rehabilitation, all in single cases, with a variety of mnemonic or perceptual approaches, and of variable efficacy. In a cohort with acquired prosopagnosia, we evaluated a perceptual learning program that incorporated variations in view and expression, which was aimed at training perceptual stages of face processing with an emphasis on ecological validity. Ten patients undertook an 11-week face training program and an 11-week control task. Training required shape discrimination between morphed facial images, whose similarity was manipulated by a staircase procedure to keep training near a perceptual threshold. Training progressed from blocks of neutral faces in frontal view through increasing variations in view and expression. Whereas the control task did not change perception, training improved perceptual sensitivity for the trained faces and generalized to new untrained expressions and views of those faces. There was also a significant transfer to new faces. Benefits were maintained over a 3-month period. Training efficacy was greater for those with more perceptual deficits at baseline. We conclude that perceptual learning can lead to persistent improvements in face discrimination in acquired prosopagnosia. This reflects both acquisition of new skills that can be applied to new faces as well as a degree of overlearning of the stimulus set at the level of 3-D expression-invariant representations.

Visual Acuity and Contrast Sensitivity Development in Children: Sweep Visually Evoked Potential and Psychophysics

The purpose of this study was to investigate the development of visual acuity (VA) and contrast sensitivity in children as measured with objective (sweep visually evoked potential) and subjective, psychophysical techniques, including signal detection theory (SDT), which attempts to control for differences in criterion or behavior between adults and children. Furthermore, this study examines the possibility of applying SDT methods with children. Visual acuity and contrast thresholds were measured in 12 children 6 to 7 years old, 10 children 8 to 9 years old, 10 children 10 to 12 years old, and 16 adults. For sweep visually evoked potential measurements, spatial frequency was swept from 1 to 40 cpd to measure VA, and contrast of sine-wave gratings (1 or 8 cpd) was swept from 0.33 to 30% to measure contrast thresholds. For psychophysical measurements, VA and contrast thresholds (1 or 8 cpd) were measured using a temporal two-alternative forced-choice staircase procedure and also with a yes-no SDT procedure. Optotype (logMAR [log of the minimum angle of resolution]) VA was also measured. The results of the various procedures were in agreement showing that there are age-related changes in threshold values and logMAR VA after the age of 6 years and that these visual functions do not become adult-like until the age of 8 to 9 years at the earliest. It was also found that children can participate in SDT procedures and do show differences in criterion compared with adults in psychophysical testing. These findings confirm a slightly later development of VA and contrast sensitivity (8 years or older) and indicate the importance of using SDT or forced-choice procedures in any developmental study to attempt to overcome the effect of criterion in children.

Camouflaging moving objects: crypsis and masquerade.

Motion is generally assumed to "break" camouflage. However, although camouflage cannot conceal a group of moving animals, it may impair a predator's ability to single one out for attack, even if that discrimination is not based on a color difference. Here, we use a computer-based task in which humans had to detect the odd one out among moving objects, with "oddity" based on shape. All objects were either patterned or plain, and either matched the background or not. We show that there are advantages of matching both group-mates and the background. However, when patterned objects are on a plain background (i.e., no background matching), the advantage of being among similarly patterned distractors is only realized when the group size is larger (10 compared to 5). In a second experiment, we present a paradigm for testing how coloration interferes with target-distractor discrimination, based on an adaptive staircase procedure for establishing the threshold. We show that when the predator only has a short time for decision-making, displaying a similar pattern to the distractors and the background affords protection even when the difference in shape between target and distractors is large. We conclude that, even though motion breaks camouflage, being camouflaged could help group-living animals reduce the risk of being singled out for attack by predators.

Seeing in the dark: Phosphene thresholds with eyes open versus closed in the absence of visual inputs

BackgroundVoluntarily opening or closing our eyes results in fundamentally different input patterns and expectancies. Yet it remains unclear how our brains and visual systems adapt to these ocular states.Objective/Hypothesis: We here used transcranial magnetic stimulation (TMS) to probe the excitability of the human visual system with eyes open or closed, in the complete absence of visual inputs. MethodsCombining Bayesian staircase procedures with computer control of TMS pulse intensity allowed interleaved determination of phosphene thresholds (PT) in both conditions. We measured parieto-occipital EEG baseline activity in several stages to track oscillatory power in the alpha (8–12 Hz) frequency-band, which has previously been shown to be inversely related to phosphene perception. ResultsSince closing the eyes generally increases alpha power, one might have expected a decrease in excitability (higher PT). While we confirmed a rise in alpha power with eyes closed, visual excitability was actually increased (PT was lower) with eyes closed. ConclusionsThis suggests that, aside from oscillatory alpha power, additional neuronal mechanisms influence the excitability of early visual cortex. One of these may involve a more internally oriented mode of brain operation, engaged by closing the eyes. In this state, visual cortex may be more susceptible to top-down inputs, to facilitate for example multisensory integration or imagery/working memory, although alternative explanations remain possible.

Application of Wald sequential test in staircase up-down adaptive procedures

An advantage of adaptive, staircase, up-down procedures in sensory threshold measurements is that such procedures are based on simple rules for signal level setting and are relatively robust to fluctuations of the subject’s attention during the measurement. A disadvantage of those procedures is that they allow to estimate the threshold level only for a few points on the psychometric function. In this study an adaptive, up-down staircase procedure is proposed which uses a decision rule based on the Wald sequential statistical test, similar to that applied in the PEST adaptive method. The Wald test allows to determine the signal threshold level for any point on the psychometric function and is simple to implement. Numerical simulations and results of an experiment performed on real subjects have shown that the staircase procedure combined with a Wald test for signal level setting reproduces the tracks of standard up-down procedures and may estimate the sensory threshold with similar accuracy. The modified procedure is thus plausible for various kind of threshold measurements in psychoacoustic studies.

Task-induced Changes in Idiopathic Infantile Nystagmus Vary with Gaze.

Investigations of infantile nystagmus syndrome (INS) at center or at the null position have reported that INS worsens when visual demand is combined with internal states, e.g. stress. Visual function and INS parameters such as foveation time, frequency, amplitude, and intensity can also be influenced by gaze position. We hypothesized that increases from baseline in visual demand and mental load would affect INS parameters at the null position differently than at other gaze positions. Eleven participants with idiopathic INS were asked to determine the direction of Tumbling-E targets, whose visual demand was varied through changes in size and contrast, using a staircase procedure. Targets appeared between ±25° in 5° steps. The task was repeated with both mental arithmetic and time restriction to impose higher mental load, confirmed through subjective ratings and concurrent physiological measurements. Within-subject comparisons were limited to the null and 15° away from it. No significant main effects of task on any INS parameters were found. At both locations, high mental load worsened task performance metrics, i.e. lowest contrast (P = .001) and smallest optotype size reached (P = .012). There was a significant interaction between mental load and gaze position for foveation time (P = .02) and for the smallest optotype reached (P = .028). The increase in threshold optotype size from the low to high mental load was greater at the null than away from it. During high visual demand, foveation time significantly decreased from baseline at the null as compared to away from it (mean difference ± SE: 14.19 ± 0.7 msec; P = .010). Under high visual demand, the effects of increased mental load on foveation time and visual task performance differed at the null as compared to 15° away from it. Assessment of these effects could be valuable when evaluating INS clinically and when considering its impact on patients' daily activities.

Psychophysical audiogram of a California sea lion (Zalophus californianus) listening for airborne tonal sounds in an acoustic chamber

Many species-typical audiograms for marine mammals are based on data from only one or a few individuals that are not always tested under ideal conditions. Here, we report auditory thresholds across the frequency range of hearing for a healthy, five-year-old female California sea lion identified as Ronan. Ronan was trained to enter a hemi-anechoic acoustic chamber to perform a go/no-go audiometric experiment. Auditory sensitivity was measured first by an adaptive staircase procedure and then by the method of constant stimuli. Minimum audible field measurements were obtained for 500 ms frequency-modulated tonal upsweeps with 10% bandwidth and 5% rise and fall times. Thresholds were measured at 13 frequencies: in one-octave frequency steps from 0.1 to 25.6 kHz, and additionally at 18.0, 22.0, 36.2, and 40.0 kHz. Sensitivity was greatest between ~0.9 and 23 kHz, with best hearing of 0 dB re 20 μPa at 12.8 kHz. Hearing range, determined at the 60 dB re 20 μPa level, extended from ~0.2 kHz to 38 kHz. Sensitivity was comparable to that of three sea lions tested in similarly controlled conditions, and much better than that of two sea lions tested in less controlled conditions. [Work supported by ONR.]

Seeing the Meaning: Top-Down Effects on Letter Identification.

Most models of reading agree that visual word recognition is underpinned by a highly interactive network in which both bottom–up and top–down processes contribute. What remains unknown is whether evidence of top–down effects upon letter processing are restricted to word-form level information, or whether meaning-level information also plays a role. Here we sought to investigate top–down semantic influences upon letter detection using semantic manipulations of real word imageability and semantic priming, as well as a manipulation of nonword orthographic and phonological composition which varied degree of similarity to real words. A continuous adaptive staircase procedure was used, allowing us to assess the exposure duration needed for accurate letter perception in different stimulus types. Results revealed that in terms of both exposure duration and decision reaction times, words showed an advantage over pseudohomophones and pseudowords, which in turn showed advantages over consonant strings. High imageability words were processed more efficiently than low imageability words, both in terms of the exposure duration required for accurate letter identification and also decision reaction times. The presence of a related as opposed to unrelated semantic prime significantly shortened exposure duration, but also lengthened decision reaction times. This inhibitory semantic priming effect in reaction time was attributed to the interference at the decision stage by stronger activation of the prime letters in the case of related relative to unrelated trials. Taken together, the present results establish for the first time that the semantic dimensions of imageability and semantic priming exert significant effects on letter identification, indicating meaning-level influences on the very earliest stages of written word recognition.

Domain-specific and domain-general processes underlying metacognitive judgments.

Metacognition and self-awareness are commonly assumed to operate as global capacities. However, there have been few attempts to test this assumption across multiple cognitive domains and metacognitive evaluations. Here, we assessed the covariance between "online" metacognitive processes, as measured by decision confidence judgments in the domains of perception and memory, and error awareness in the domain of attention to action. Previous research investigating metacognition across task domains have not matched stimulus characteristics across tasks raising the possibility that any differences in metacognitive accuracy may be influenced by local task properties. The current experiment measured metacognition in perceptual, memorial and attention tasks that were closely matched for stimulus characteristics. We found that metacognitive accuracy across the three tasks was dissociated suggesting that domain specific networks support an individual's capacity for accurate metacognition. This finding was independent of objective performance, which was controlled using a staircase procedure. However, response times for metacognitive judgments and error awareness were associated suggesting that shared mechanisms determining how these meta-level evaluations unfold in time may underlie these different types of decision. In addition, the relationship between these laboratory measures of metacognition and reports of everyday functioning from participants and their significant others (informants) was investigated. We found that informant reports, but not self reports, predicted metacognitive accuracy on the perceptual task and participants who underreported cognitive difficulties relative to their informants also showed poorer metacognitive accuracy on the perceptual task. These results are discussed in the context of models of metacognitive regulation and neuropsychological evidence for dissociable metacognitive systems. The potential for the refinement of metacognitive assessment in clinical populations is also discussed.