The phase coherence of cortical oscillations predicts dynamic changes in perceived visibility.

The phase synchronization of brain oscillations plays an important role in visual processing, perceptual awareness, and performance. Yet, the cortical mechanisms underlying modulatory effects of post-stimulus phase coherence and frequency-specific oscillations associated with different aspects of vision are still subject to debate. In this study, we aimed to identify the post-stimulus phase coherence of cortical oscillations associated with perceived visibility and contour discrimination. We analyzed electroencephalogram data from two masking experiments where target visibility was manipulated by the contrast ratio or polarity of the mask under various onset timing conditions (stimulus onset asynchronies, SOAs). The behavioral results indicated an SOA-dependent suppression of target visibility due to masking. The time-frequency analyses revealed significant modulations of phase coherence over occipital and parieto-occipital regions. We particularly identified modulations of phase coherence in the (i) 2-5 Hz frequency range, which may reflect feedforward-mediated contour detection and sustained visibility; and (ii) 10-25 Hz frequency range, which may be associated with suppressed visibility through inhibitory interactions between and within synchronized neural pathways. Taken together, our findings provide evidence that oscillatory phase alignments, not only in the pre-stimulus but also in the post-stimulus window, play a crucial role in shaping perceived visibility and dynamic vision.

Pupil Size and Eye Movements Differently Index Effort in Both Younger and Older Adults.

The assessment of mental effort is increasingly relevant in neurocognitive and life span domains. Pupillometry, the measure of the pupil size, is often used to assess effort but has disadvantages. Analysis of eye movements may provide an alternative, but research has been limited to easy and difficult task demands in younger adults. An effort measure must be sensitive to the whole effort profile, including "giving up" effort investment, and capture effort in different age groups. The current study comprised three experiments in which younger (n = 66) and older (n = 44) adults listened to speech masked by background babble at different signal-to-noise ratios associated with easy, difficult, and impossible speech comprehension. We expected individuals to invest little effort for easy and impossible speech (giving up) but to exert effort for difficult speech. Indeed, pupil size was largest for difficult but lower for easy and impossible speech. In contrast, gaze dispersion decreased with increasing speech masking in both age groups. Critically, gaze dispersion during difficult speech returned to levels similar to easy speech after sentence offset, when acoustic stimulation was similar across conditions, whereas gaze dispersion during impossible speech continued to be reduced. These findings show that a reduction in eye movements is not a byproduct of acoustic factors, but instead suggest that neurocognitive processes, different from arousal-related systems regulating the pupil size, drive reduced eye movements during high task demands. The current data thus show that effort in one sensory domain (audition) differentially impacts distinct functional properties in another sensory domain (vision).

Neural encoding for spatial release from informational masking and its correlation with behavioral metrics.

The central auditory system encompasses two primary functions: identification and localization. Spatial release from masking (SRM) highlights speech recognition in competing noise and improves the listening experience when a spatial cue is introduced between noise and target speech. This assessment focuses on the integrity of auditory function and holds clinical significance. However, infants or pre-lingual subjects sometimes provide less reliable results. This study investigates the value of cortical auditory evoked potentials (CAEPs) onset and acoustic change complex (ACC) as an objective measurement of SRM. Thirty normal-hearing young adults (11 males) were recruited. We found the spatial separation of signals and noise (±90° symmetrically) resulted in a signal-to-noise ratio (SNR) improvement of 9.00 ± 1.71 dB behaviorally. It significantly enhanced cortical processing at all SNR levels, shortened CAEP latencies, and increased amplitudes, resulting in a greater number of measurable peaks for ACC. SRM showed mild to moderate correlations with the differences between two conditions in CAEP measures. The regression model combining N1'-P2' amplitude at 5 dB SNR (R2 = 0.26), P1 amplitude at 0 dB SNR (R2 = 0.14), and P1 latency at -5 dB SNR (R2 = 0.15), explained 45.3% of the variance in SRM. Our study demonstrates that introducing spatial cues can improve speech perception and enhance central auditory processing in normal-hearing young adults. CAEPs may contribute to predictions about SRM and hold potential for practical application.NEW & NOTEWORTHY The neural encoding of spatial release from masking (SRM) can be observed in normal-hearing young adults. Spatial separation between target and masker improves speech perception in noise and enhances central auditory processing. The behavioral results showed mild-to-moderate correlations with electrophysiological measures, with acoustic change complex (ACC) amplitude being a better indicator than onset components. Cortical auditory evoked potentials (CAEPs) may contribute to predictions about spatial release from masking, especially when behavioral tests are less reliable.

Modeling bee movement shows how a perceptual masking effect can influence flower discovery.

Understanding how pollinators move across space is key to understanding plant mating patterns. Bees are typically assumed to search for flowers randomly or using simple movement rules, so that the probability of discovering a flower should primarily depend on its distance to the nest. However, experimental work shows this is not always the case. Here, we explored the influence of flower size and density on their probability of being discovered by bees by developing a movement model of central place foraging bees, based on experimental data collected on bumblebees. Our model produces realistic bee trajectories by taking into account the autocorrelation of the bee's angular speed, the attraction to the nest (homing), and a gaussian noise. Simulations revealed a « masking effect ¼ that reduces the detection of flowers close to another, with potential far reaching consequences on plant-pollinator interactions. At the plant level, flowers distant to the nest were more often discovered by bees in low density environments. At the bee colony level, foragers found more flowers when they were small and at medium densities. Our results indicate that the processes of search and discovery of resources are potentially more complex than usually assumed, and question the importance of resource distribution and abundance on bee foraging success and plant pollination.

Masked Speech Perception with Bone Conduction Device, Contralateral Routing of Signals Hearing Aid, and Cochlear Implant Use in Adults with Single-Sided Deafness: A Prospective Hearing Device Comparison using a Unified Testing Framework.

INTRODUCTION: For the treatment of single-sided deafness (SSD), common treatment choices include a contralateral routing of signals (CROS) hearing aid, a bone conduction device (BCD), and a cochlear implant (CI). The primary aim of this study was to compare speech understanding in noise and binaural benefits in adults with postlingual SSD between preoperative unaided baseline, preoperative CROS and BCD trial devices, and CI, following recommendations from a consensus protocol. In addition, we investigated the effect of masker type on speech understanding. METHODS: This was a prospective study with twelve participants. Binaural effects of head shadow, squelch, summation, and spatial release from masking were assessed by measuring speech reception thresholds (SRTs) in five different spatial target-masker configurations using two different maskers: two-talker babble (TTB), and speech-shaped noise (SSN). Preoperatively, participants were assessed unaided and with CROS and BCD trial devices. After cochlear implantation, participants were assessed at 1, 3, and 6 months post-activation. RESULTS: For TTB, significant improvements in SRT with a CI relative to preoperatively unaided were found in all spatial configurations. With CI at 6 months, median benefits were 7.8 dB in SSSDNAH and 5.1 dB in S0NAH (head shadow), 3.4 dB in S0N0 (summation), and 4.6 dB in S0NSSD and 5.1 dB in SAHNSSD (squelch). CROS yielded a significant head shadow benefit of 2.4 dB in SSSDNAH and a significant deterioration in squelch of 2.5 dB in S0NSSD and SAHNSSD, but no summation effect. With BCD, there was a significant summation benefit of 1.5 dB, but no head shadow nor squelch effect. For SSN, significant improvements in SRT with CI compared to preoperatively unaided were found in three spatial configurations. Median benefits with CI at 6 months were: 8.5 dB in SSSDNAH and 4.6 dB in S0NAH (head shadow), 1.4 dB in S0N0 (summation), but no squelch. CROS showed a significant head shadow benefit of 1.7 dB in SSSDNAH, but no summation effect, and a significant deterioration in squelch of 2.9 dB in S0NSSD and 3.2 dB in SAHNSSD. With BCD, no binaural effect was obtained. Longitudinally, we found significant head shadow benefits with a CI in SSSDNAH in both maskers at all postoperative intervals and in S0NAH at 3 and 6 months post-activation. CONCLUSION: With a CI, a clear benefit for masked speech perception was observed for all binaural effects. Benefits with CROS and BCD were more limited. CROS usage was detrimental to the squelch effect.

Predictors of Susceptibility to Noise and Speech Masking Among School-Age Children With Hearing Loss or Typical Hearing.

OBJECTIVES: The purpose of this study was to evaluate effects of masker type and hearing group on the relationship between school-age children's speech recognition and age, vocabulary, working memory, and selective attention. This study also explored effects of masker type and hearing group on the time course of maturation of masked speech recognition. DESIGN: Participants included 31 children with normal hearing (CNH) and 41 children with mild to severe bilateral sensorineural hearing loss (CHL), between 6.7 and 13 years of age. Children with hearing aids used their personal hearing aids throughout testing. Audiometric thresholds and standardized measures of vocabulary, working memory, and selective attention were obtained from each child, along with masked sentence recognition thresholds in a steady state, speech-spectrum noise (SSN) and in a two-talker speech masker (TTS). Aided audibility through children's hearing aids was calculated based on the Speech Intelligibility Index (SII) for all children wearing hearing aids. Linear mixed effects models were used to examine the contribution of group, age, vocabulary, working memory, and attention to individual differences in speech recognition thresholds in each masker. Additional models were constructed to examine the role of aided audibility on masked speech recognition in CHL. Finally, to explore the time course of maturation of masked speech perception, linear mixed effects models were used to examine interactions between age, masker type, and hearing group as predictors of masked speech recognition. RESULTS: Children's thresholds were higher in TTS than in SSN. There was no interaction of hearing group and masker type. CHL had higher thresholds than CNH in both maskers. In both hearing groups and masker types, children with better vocabularies had lower thresholds. An interaction of hearing group and attention was observed only in the TTS. Among CNH, attention predicted thresholds in TTS. Among CHL, vocabulary and aided audibility predicted thresholds in TTS. In both maskers, thresholds decreased as a function of age at a similar rate in CNH and CHL. CONCLUSIONS: The factors contributing to individual differences in speech recognition differed as a function of masker type. In TTS, the factors contributing to individual difference in speech recognition further differed as a function of hearing group. Whereas attention predicted variance for CNH in TTS, vocabulary and aided audibility predicted variance in CHL. CHL required a more favorable signal to noise ratio (SNR) to recognize speech in TTS than in SSN (mean = +1 dB in TTS, -3 dB in SSN). We posit that failures in auditory stream segregation limit the extent to which CHL can recognize speech in a speech masker. Larger sample sizes or longitudinal data are needed to characterize the time course of maturation of masked speech perception in CHL.

Development of the Children's English and Spanish Speech Recognition Test: Psychometric Properties, Feasibility, Reliability, and Normative Data.

OBJECTIVES: The Children's English and Spanish Speech Recognition (ChEgSS) test is a computer-based tool for assessing closed-set word recognition in English and in Spanish, with a masker that is either speech-shaped noise or competing speech. The present study was conducted to (1) characterize the psychometric properties of the ChEgSS test, (2) evaluate feasibility and reliability for a large cohort of Spanish/English bilingual children with normal hearing, and (3) establish normative data. DESIGN: Three experiments were conducted to evaluate speech perception in children (4-17 years) and adults (19-40 years) with normal hearing using the ChEgSS test. In Experiment 1, data were collected from Spanish/English bilingual and English monolingual adults at multiple, fixed signal-to-noise ratios. Psychometric functions were fitted to the word-level data to characterize variability across target words in each language and in each masker condition. In Experiment 2, Spanish/English bilingual adults were tested using an adaptive tracking procedure to evaluate the influence of different target-word normalization approaches on the reliability of estimates of masked-speech recognition thresholds corresponding to 70.7% correct word recognition and to determine the optimal number of reversals needed to obtain reliable estimates. In Experiment 3, Spanish/English bilingual and English monolingual children completed speech perception testing using the ChEgSS test to (1) characterize feasibility across age and language group, (2) evaluate test-retest reliability, and (3) establish normative data. RESULTS: Experiments 1 and 2 yielded data that are essential for stimulus normalization, optimizing threshold estimation procedures, and interpreting threshold data across test language and masker type. Findings obtained from Spanish/English bilingual and English monolingual children with normal hearing in Experiment 3 support feasibility and demonstrate reliability for use with children as young as 4 years of age. Equivalent results for testing in English and Spanish were observed for Spanish/English bilingual children, contingent on adequate proficiency in the target language. Regression-based threshold norms were established for Spanish/English bilingual and English monolingual children between 4 and 17 years of age. CONCLUSIONS: The present findings indicate the ChEgSS test is appropriate for testing a wide age range of children with normal hearing in either Spanish, English, or both languages. The ChEgSS test is currently being evaluated in a large cohort of patients with hearing loss at pediatric audiology clinics across the United States. Results will be compared with normative data established in the present study and with established clinical measures used to evaluate English- and Spanish-speaking children. Questionnaire data from parents and clinician feedback will be used to further improve test procedures.

Midlife Speech Perception Deficits: Impact of Extended High-Frequency Hearing, Peripheral Neural Function, and Cognitive Abilities.

OBJECTIVES: The objectives of the present study were to investigate the effects of age-related changes in extended high-frequency (EHF) hearing, peripheral neural function, working memory, and executive function on speech perception deficits in middle-aged individuals with clinically normal hearing. DESIGN: We administered a comprehensive assessment battery to 37 participants spanning the age range of 20 to 56 years. This battery encompassed various evaluations, including standard and EHF pure-tone audiometry, ranging from 0.25 to 16 kHz. In addition, we conducted auditory brainstem response assessments with varying stimulation rates and levels, a spatial release from masking (SRM) task, and cognitive evaluations that involved the Trail Making test (TMT) for assessing executive function and the Abbreviated Reading Span test (ARST) for measuring working memory. RESULTS: The results indicated a decline in hearing sensitivities at EHFs and an increase in completion times for the TMT with age. In addition, as age increased, there was a corresponding decrease in the amount of SRM. The declines in SRM were associated with age-related declines in hearing sensitivity at EHFs and TMT performance. While we observed an age-related decline in wave I responses, this decline was primarily driven by age-related reductions in EHF thresholds. In addition, the results obtained using the ARST did not show an age-related decline. Neither the auditory brainstem response results nor ARST scores were correlated with the amount of SRM. CONCLUSIONS: These findings suggest that speech perception deficits in middle age are primarily linked to declines in EHF hearing and executive function, rather than cochlear synaptopathy or working memory.

How (not) to demonstrate unconscious priming: Overcoming issues with post-hoc data selection, low power, and frequentist statistics.

One widely used scientific approach to studying consciousness involves contrasting conscious operations with unconscious ones. However, challenges in establishing the absence of conscious awareness have led to debates about the extent and existence of unconscious processes. We collected experimental data on unconscious semantic priming, manipulating prime presentation duration to highlight the critical role of the analysis approach in attributing priming effects to unconscious processing. We demonstrate that common practices like post-hoc data selection, low statistical power, and frequentist statistical testing can erroneously support claims of unconscious priming. Conversely, adopting best practices like direct performance-awareness contrasts, Bayesian tests, and increased statistical power can prevent such erroneous conclusions. Many past experiments, including our own, fail to meet these standards, casting doubt on previous claims about unconscious processing. Implementing these robust practices will enhance our understanding of unconscious processing and shed light on the functions and neural mechanisms of consciousness.

Pupil dilation reflects covert familiar face recognition under interocular suppression.

In prosopagnosia, brain lesions impair overt face recognition, but not face detection, and may coexist with residual covert recognition of familiar faces. Previous studies that simulated covert recognition in healthy individuals have impaired face detection as well as recognition, thus not fully mirroring the deficits in prosopagnosia. We evaluated a model of covert recognition based on continuous flash suppression (CFS). Familiar and unfamiliar faces and houses were masked while participants performed two discrimination tasks. With increased suppression, face/house discrimination remained largely intact, but face familiarity discrimination deteriorated. Covert recognition was present across all masking levels, evinced by higher pupil dilation to familiar than unfamiliar faces. Pupil dilation was uncorrelated with overt performance across subjects. Thus, CFS can impede overt face recognition without disrupting covert recognition and face detection, mirroring critical features of prosopagnosia. CFS could be used to uncover shared neural mechanisms of covert recognition in prosopagnosic patients and neurotypicals.

Prime-induced illusion of control: The influence of unconscious priming on self-initiated actions and the role of regression to the mean.

To what degree human cognition is influenced by subliminal stimuli is a controversial empirical question. One striking example was reported by Linser and Goschke (2007): participants overestimated how much control they had over objectively uncontrollable stimuli when masked congruent primes were presented immediately before the action. Critically, however, unawareness of the masked primes was established by post hoc data selection. In our preregistered study we sought to explore these findings while adjusting prime visibility based on individual thresholds, so that each participant underwent both visible and non-visible conditions. In experiment 1, N = 39 participants engaged in a control judgement task: following the presentation of a semantic prime, they freely selected between two keys, which triggered the appearance of a colored circle. The color of the circles, however, was independent of the key-press. Subsequently, participants assessed their perceived control over the circle's color, based on their key-presses, via a rating scale that ranged from 0 % (no control) to 100 % (complete control). Contrary to Linser and Goschke (2007)'s findings, this experiment demonstrated that predictive information influenced the experience of agency only when primes were consciously processed. In experiment 2, utilizing symbolic (arrow) primes, N = 35 participants had to rate their feeling of control over the effect-stimulus' identity during a two-choice identification paradigm (i.e., they were instructed to press a key corresponding to a target stimulus; with a contingency between target and effect stimulus of 75 %/25 %). The results revealed no significant influence of subliminal priming on agency perceptions. In summary, this study implies that unconscious stimuli may not exert a substantial influence on the conscious experience of agency, underscoring the need for careful consideration of methodological aspects and experimental design's impact on observed phenomena.

Masks wearing off: Changing effects of face masks on trustworthiness over time.

During the global COVID-19 pandemic, the wearing of face masks became a common practice, raising questions about how masks affect perceptions of and behaviour towards others. Numerous studies have explored the impact of face masks on perceptions of trustworthiness, but results have been mixed and it remains unclear whether masks influence perceptions via their social meaning or their effects on facial appearance. In this study, Australian participants (N = 363) rated a series of faces which were either masked, unmasked, or occluded by a non-mask object (computer) in terms of perceived trustworthiness in 2020, 2022, or 2023. The apparent trustworthiness of unmasked faces remained stable across years, but masked faces were rated significantly more trustworthy in 2020 compared to 2022 and 2023. Furthermore, ratings of masked faces, but not unmasked faces, were correlated with participants' attitudes towards wearing masks. Faces occluded by a non-mask object were perceived to be less trustworthy than masked faces. Together, results strongly suggest the increase in perceived trustworthiness of masked faces reported in numerous studies conducted during COVID-19 were driven by positive social meanings around mask wearing rather than by their effect on facial appearance.

Perception of invisible masked objects in early infancy.

Recurrent loops in the visual cortex play a critical role in visual perception, which is likely not mediated by purely feed-forward pathways. However, the development of recurrent loops is poorly understood. The role of recurrent processing has been studied using visual backward masking, a perceptual phenomenon in which a visual stimulus is rendered invisible by a following mask, possibly because of the disruption of recurrent processing. Anatomical studies have reported that recurrent pathways are immature in early infancy. This raises the possibility that younger infants process visual information mainly in a feed-forward manner, and thus, they might be able to perceive visual stimuli that adults cannot see because of backward masking. Here, we show that infants under 7 mo of age are immune to visual backward masking and that masked stimuli remain visible to younger infants while older infants cannot perceive them. These results suggest that recurrent processing is immature in infants under 7 mo and that they are able to perceive objects even without recurrent processing. Our findings indicate that the algorithm for visual perception drastically changes in the second half of the first year of life.

Testing models at the neural level reveals how the brain computes subjective value.

Decisions are based on the subjective values of choice options. However, subjective value is a theoretical construct and not directly observable. Strikingly, distinct theoretical models competing to explain how subjective values are assigned to choice options often make very similar behavioral predictions, which poses a major difficulty for establishing a mechanistic, biologically plausible explanation of decision-making based on behavior alone. Here, we demonstrate that model comparison at the neural level provides insights into model implementation during subjective value computation even though the distinct models parametrically identify common brain regions as computing subjective value. We show that frontal cortical regions implement a model based on the statistical distributions of available rewards, whereas intraparietal cortex and striatum compute subjective value signals according to a model based on distortions in the representations of probabilities. Thus, better mechanistic understanding of how cognitive processes are implemented arises from model comparisons at the neural level, over and above the traditional approach of comparing models at the behavioral level alone.

Evaluating integration of letter fragments through contrast and spatially targeted masking.

Four experiments were conducted to gain a better understanding of the visual mechanisms related to how integration of partial shape cues provides for recognition of the full shape. In each experiment, letters formed as outline contours were displayed as a sequence of adjacent segments (fragments), each visible during a 17-ms time frame. The first experiment varied the contrast of the fragments. There were substantial individual differences in contrast sensitivity, so stimulus displays in the masking experiments that followed were calibrated to the sensitivity of each participant. Masks were displayed either as patterns that filled the entire screen (full field) or as successive strips that were sliced from the pattern, each strip lying across the location of the letter fragment that had been shown a moment before. Contrast of masks were varied to be lighter or darker than the letter fragments. Full-field masks, whether light or dark, provided relatively little impairment of recognition, as was the case for mask strips that were lighter than the letter fragments. However, dark strip masks proved to be very effective, with the degree of recognition impairment becoming larger as mask contrast was increased. A final experiment found the strip masks to be most effective when they overlapped the location where the letter fragments had been shown a moment before. They became progressively less effective with increased spatial separation from that location. Results are discussed with extensive reference to potential brain mechanisms for integrating shape cues.

Speech intelligibility and its relation to auditory temporal processing in Czech and Swiss German subjects with and without tinnitus.

PURPOSE: Previous studies have shown that levels for 50% speech intelligibility in quiet and in noise differ for different languages. Here, we aimed to find out whether these differences may relate to different auditory processing of temporal sound features in different languages, and to determine the influence of tinnitus on speech comprehension in different languages. METHODS: We measured speech intelligibility under various conditions (words in quiet, sentences in babble noise, interrupted sentences) along with tone detection thresholds in quiet [PTA] and in noise [PTAnoise], gap detection thresholds [GDT], and detection thresholds for frequency modulation [FMT], and compared them between Czech and Swiss subjects matched in mean age and PTA. RESULTS: The Swiss subjects exhibited higher speech reception thresholds in quiet, higher threshold speech-to-noise ratio, and shallower slope of performance-intensity function for the words in quiet. Importantly, the intelligibility of temporally gated speech was similar in the Czech and Swiss subjects. The PTAnoise, GDT, and FMT were similar in the two groups. The Czech subjects exhibited correlations of the speech tests with GDT and FMT, which was not the case in the Swiss group. Qualitatively, the results of comparisons between the Swiss and Czech populations were not influenced by presence of subjective tinnitus. CONCLUSION: The results support the notion of language-specific differences in speech comprehension which persists also in tinnitus subjects, and indicates different associations with the elementary measures of auditory temporal processing.

The radial-tangential anisotropy of numerosity perception.

Humans can estimate the number of visually presented items without counting. In most studies on numerosity perception, items are uniformly distributed across displays, with identical distributions in central and eccentric parts. However, the neural and perceptual representation of the human visual field differs between the fovea and the periphery. For example, in peripheral vision, there are strong asymmetries with regard to perceptual interferences between visual items. In particular, items arranged radially usually interfere more strongly with each other than items arranged tangentially (the radial-tangential anisotropy). This has been shown for crowding (the deleterious effect of clutter on target identification) and redundancy masking (the reduction of the number of perceived items in repeating patterns). In the present study, we tested how the radial-tangential anisotropy of peripheral vision impacts numerosity perception. In four experiments, we presented displays with varying numbers of discs that were predominantly arranged radially or tangentially, forming strong and weak interference conditions, respectively. Participants were asked to report the number of discs. We found that radial displays were reported as less numerous than tangential displays for all radial and tangential manipulations: weak (Experiment 1), strong (Experiment 2), and when using displays with mixed contrast polarity discs (Experiments 3 and 4). We propose that numerosity perception exhibits a significant radial-tangential anisotropy, resulting from local spatial interactions between items.

Flicker adaptation improves acuity for briefly presented stimuli by reducing crowding.

Adaptation to flickering/dynamic noise improves visual acuity for briefly presented stimuli (Arnold et al., 2016). Here, we investigate whether such adaptation operates directly on our ability to see detail or by changing fixational eye movements and pupil size or by reducing visual crowding. Following earlier work, visual acuity was measured in observers who were either unadapted or who had adapted to a 60-Hz flickering noise pattern. Participants reported the orientation of a white tumbling-T target (four-alternative forced choice [4AFC], ⊤⊣⊥⊢). The target was presented for 110 ms either in isolation or flanked by randomly oriented T's (e.g., ⊣⊤⊢) followed by an isolated (+) or flanked (+++) mask, respectively. We measured fixation stability (using an infrared eye tracker) while observers performed the task (with and without adaptation). Visual acuity improved modestly (around 8.4%) for flanked optotypes following adaptation to flicker (mean, -0.038 ± 0.063 logMAR; p = 0.015; BF10 = 3.66) but did not when measured with isolated letters (mean, -0.008 ± 0.055 logMAR; p = 0.5; BF10 = 0.29). The magnitude of acuity improvement was associated with individuals' (unadapted) susceptibility to crowding (the ratio of crowded to uncrowded acuity; r = -0.58, p = 0.008, BF10 = 7.70) but to neither fixation stability nor pupil size. Confirming previous reports, flicker improved acuity for briefly presented stimuli, but we show that this was only the case for crowded letters. These improvements likely arise from attenuation of sensitivity to a transient low spatial frequency (SF) image structure (Arnold et al., 2016; Tagoh et al., 2022), which may, for example, reduce masking of high SFs by low SFs. We also suggest that this attenuation could reduce backward masking and so reduce foveal crowding.

Serial dependence requires visual awareness: Evidence from continuous flash suppression.

The visual system often undergoes a relatively stable perception even in a noisy visual environment. This crucial function was reflected in a visual perception phenomenon-serial dependence, in which recent stimulus history systematically biases current visual decisions. Although serial dependence effects have been revealed in numerous studies, few studies examined whether serial dependence would require visual awareness. By using the continuous flash suppression (CFS) technique to render grating stimuli invisible, we investigated whether serial dependence effects could emerge at the unconscious levels. In an orientation adjustment task, subjects viewed a randomly oriented grating and reported their orientation perception via an adjustment response. Subjects performed a series of three type trial pairs. The first two trial pairs, in which subjects were instructed to make a response or no response toward the first trial of the pairs, respectively, were used to measure serial dependence at the conscious levels; the third trial pair, in which the grating stimulus in the first trial of the pair was masked by a CFS stimulus, was used to measure the serial dependence at the unconscious levels. One-back serial dependence effects for the second trial of the pairs were evaluated. We found significant serial dependence effects at the conscious levels, whether absence (Experiment 1) or presence (Experiment 2) of CFS stimuli, but failed to find the effects at the unconscious levels, corroborating the view that serial dependence requires visual awareness.

Facial ambiguity and perception: How face-likeness affects breaking time in continuous flash suppression.

Previous studies have elucidated that humans can implicitly process faces faster than they process objects. However, the mechanism through which the brain unconsciously processes ambiguous facial images remains unclear. In our experiment, upright and inverted black-and-white binary face stimuli were presented in a two-alternative forced-choice location discrimination task combined with continuous flash suppression, a technique that suppresses visual stimuli perception using rapidly changing masks. The breaking time (BT) or the time required for a stimulus to be perceptually recognized was recorded for each face stimulus. The results showed that the BT for inverted grayscale images was significantly longer than that for upright grayscale faces, whereas the BT for upright and inverted binary faces did not reach statistical significance. A significant correlation between face likeness and BT was established after evaluating face likeness for each binary face stimulus, with high-face-like binary faces exhibiting shorter BT and low-face-like stimuli resulting in a more prolonged BT. Our results suggest that even an ambiguous object rated highly in face likeness can reduce the BT under implicit processing, indicating the possibility that facial parts such as the eyes and nose are subconsciously detected in ambiguous facial stimuli, enabling facial perception.