Multisensory-mediated auditory localization

Multisensory integration is a powerful mechanism for maximizing sensitivity to sensory events. We examined its effects on auditory localization in healthy human subjects. The specific objective was to test whether the relative intensity and location of a seemingly irrelevant visual stimulus would influence auditory localization in accordance with the inverse effectiveness and spatial rules of multisensory integration that have been developed from neurophysiological studies with animals [Stein and Meredith, 1993 The Merging of the Senses (Cambridge, MA: MIT Press)]. Subjects were asked to localize a sound in one condition in which a neutral visual stimulus was either above threshold (supra-threshold) or at threshold. In both cases the spatial disparity of the visual and auditory stimuli was systematically varied. The results reveal that stimulus salience is a critical factor in determining the effect of a neutral visual cue on auditory localization. Visual bias and, hence, perceptual translocation of the auditory stimulus appeared when the visual stimulus was supra-threshold, regardless of its location. However, this was not the case when the visual stimulus was at threshold. In this case, the influence of the visual cue was apparent only when the two cues were spatially coincident and resulted in an enhancement of stimulus localization. These data suggest that the brain uses multiple strategies to integrate multisensory information.     

Visual form recognition threshold and the psychological refractory period

Two experiments studied the effect of a reaction time response (RT) on visual form recognition threshold when the temporal interval separating the RT stimulus and the recognition stimulus was short. In Experiment 1 an initial RT response to an auditory signal did not impair the subsequent forced-choice visual form recognition threshold. Interstimulus intervals (ISI) of 0, 50, 100, 150, and 200 msec were used; S was always aware of the ISI under test. In Experiment 2 a visual stimulus was used to elicit the R T response; this shift to an intramodal stimulus did not alter the recognition threshold. These data were interpreted as supporting the hypothesis that two stimulus events can be processed simultaneously even when the temporal interval between them is short.     

Visual contribution to human standing balance during support surface tilts

Visual position and velocity cues improve human standing balance, reducing sway responses to external disturbances and sway variability. Previous work suggested that human balancing is based on sensory estimates of external disturbances and their compensation using feedback mechanisms (Disturbance Estimation and Compensation, DEC model). This study investigates the visual effects on sway responses to pseudo-random support surface tilts, assuming that improvements result from lowering the velocity threshold in a tilt estimate and the position threshold in an estimate of the gravity disturbance. Center of mass (COM) sway was measured with four different tilt amplitudes, separating the effect of visual cues across the conditions ‘Eyes closed’ (no visual cues), ‘4 Hz stroboscopic illumination’ (visual position cues), and ‘continuous illumination’ (visual position and velocity cues). In a model based approach, parameters of disturbance estimators were identified. The model reproduced experimental results and showed a specific reduction of the position and velocity threshold when adding visual position and velocity cues, respectively. Sway variability was analyzed to explore a hypothesized relation between estimator thresholds and internal noise. Results suggest that adding the visual cues reduces the contribution of vestibular noise, thereby reducing sway variability and allowing for lower thresholds, which improves the disturbance compensation.     

Video game experience and its influence on visual attention parameters: An investigation using the framework of the Theory of Visual Attention (TVA)

Experts with video game experience, in contrast to non-experienced persons, are superior in multiple domains of visual attention. However, it is an open question which basic aspects of attention underlie this superiority. We approached this question using the framework of Theory of Visual Attention (TVA) with tools that allowed us to assess various parameters that are related to different visual attention aspects (e.g., perception threshold, processing speed, visual short-term memory storage capacity, top-down control, spatial distribution of attention) and that are measurable on the same experimental basis. In Experiment 1, we found advantages of video game experts in perception threshold and visual processing speed; the latter being restricted to the lower positions of the used computer display. The observed advantages were not significantly moderated by general person-related characteristics such as personality traits, sensation seeking, intelligence, social anxiety, or health status. Experiment 2 tested a potential causal link between the expert advantages and video game practice with an intervention protocol. It found no effects of action video gaming on perception threshold, visual short-term memory storage capacity, iconic memory storage, top-down control, and spatial distribution of attention after 15 days of training. However, observations of a selected improvement of processing speed at the lower positions of the computer screen after video game training and of retest effects are suggestive for limited possibilities to improve basic aspects of visual attention (TVA) with practice.     

Good vibrations: Human interval timing in the vibrotactile modality

This article reports a detailed examination of timing in the vibrotactile modality and comparison with that of visual and auditory modalities. Three experiments investigated human timing in the vibrotactile modality. In Experiment 1, a staircase threshold procedure with a standard duration of 1,000 ms revealed a difference threshold of 160.35 ms for vibrotactile stimuli, which was significantly higher than that for auditory stimuli (103.25 ms) but not significantly lower than that obtained for visual stimuli (196.76 ms). In Experiment 2, verbal estimation revealed a significant slope difference between vibrotactile and auditory timing, but not between vibrotactile and visual timing. That is, both vibrations and lights were judged as shorter than sounds, and this comparative difference was greater at longer durations than at shorter ones. In Experiment 3, performance on a temporal generalization task showed characteristics consistent with the predications of scalar expectancy theory (SET: Gibbon, 1977) with both mean accuracy and scalar variance exhibited. The results were modelled using the modified Church and Gibbon model (MCG; derived by Wearden, 1992, from Church & Gibbon 1982). The model was found to give an excellent fit to the data, and the parameter values obtained were compared with those for visual and auditory temporal generalization. The pattern of results suggest that timing in the vibrotactile modality conforms to SET and that the internal clock speed for vibrotactile stimuli is significantly slower than that for auditory stimuli, which is logically consistent with the significant differences in difference threshold that were obtained.     

The effect of white-noise mask level on sinewave contrast detection thresholds and the critical-band-masking model

It is known that visual noise added to sinusoidal gratings changes the typical U-shaped threshold curve which becomes flat in log-log scale for frequencies below 10c/deg when gratings are masked with white noise of high power spectral density level. These results have been explained using the critical-band-masking (CBM) model by supposing a visual filter-bank of constant relative bandwidth. However, some psychophysical and biological data support the idea of variable octave bandwidth. The CBM model has been used here to explain the progressive change of threshold curves with the noise mask level and to estimate the bandwidth of visual filters. Bayesian staircases were used in a 2IFC paradigm to measure contrast thresholds of horizontal sinusoidal gratings (0.25-8 c/deg) within a fixed Gaussian window and masked with one-dimensional, static, broadband white noise with each of five power density levels. Raw data showed that the contrast threshold curve progressively shifts upward and flattens out as the mask noise level increases. Theoretical thresholds from the CBM model were fitted simultaneously to the data at all five noise levels using visual filters with log-Gaussian gain functions. If we assume a fixed-channel detection model, the best fit was obtained when the octave bandwidth of visual filters decreases as a function of peak spatial frequency.     

Visual influence on taste sensitivity

A claimed dependence of taste sensitivity on body state, accepted for 40 years, is investigated in two experiments. Neither the growth of sensation above threshold, as measured in a magnitude estimation experiment, nor taste sensitivity near threshold, as measured by a signal detection analysis, show the claimed increment when individuals are dark-adapted. On the contrary, in both cases, performance is superior in the light, when subjects taste with their eyes open, possibly due to an arousing effect of concurrent visual stimulation.     

Being confident without seeing: What subjective measures of visual consciousness are about

Can observers be confident about the accuracy of a discrimination response without a visual experience of the stimulus? In a series of five experiments, observers performed a masked orientation discrimination task, a masked shape discrimination task, or a random-dot motion discrimination task, followed by two subjective ratings after each trial, in which participants reported either their visual experience of the stimulus or their confidence in being correct. We observed that the threshold for ratings of the perception of the stimulus was above the threshold for ratings of a decision, that decision ratings outperformed stimulus ratings in predicting trial accuracy, and that different decision-related scales were more strongly associated with other decision-related scales than with ratings of stimulus clarity. We propose a taxonomy of subjective measures of consciousness that differentiates between subjective measures relating to the percept of the stimulus and measures relating to a discrimination decision and discuss the relation to type II blindsight.     

动态视觉加工与儿童汉字阅读

使用视觉阈限测验、图片命名、字形相似性判断实验和语音意识等测验 ,考察了小学五年级儿童视觉加工技能与汉字阅读之间的关系。结果发现 :动态视觉加工与图片命名错误率、字形判断反应时和错误率、语音意识均有显著相关 ,静态视觉加工只与图片命名错误率相关显著 ;控制识字量后的偏相关分析显示 ,动态视觉加工与其他变量的相关关系不变 ,静态视觉加工与图片命名错误率的相关不再显著 ;回归分析发现动态视觉加工在识字量和语音意识的影响控制后 ,能够分别解释阅读流畅性、字形判断反应时和图片命名错误率 7%、2 5 %和 5 6 %的变化 ;语音意识能够解释识字量和阅读流畅性 9%和 10 %的变化 ;对差读者的动态视觉加工和语音意识分析发现 ,儿童在这两种测验上的个体差异很大。上述结果表明 ,阅读过程受基本知觉技能影响 ,动态视觉加工作用于汉字阅读的特定过程。     

The effect of an after-coming random pattern on the perception of brief visual stimuli

The perception of briefly exposed visual forms is shown to be masked by an after- coming random pattern stimulus of approximately equal intensity. This effect occurs only under certain well defined conditions; it is limited by the minimum stimulus exposure time in excess of threshold which overcomes masking (critical stimulus duration) as well as by the minimum interval between presentation of the two stimuli which permits evasion of the masking action (critical interval). Over the range of stimulus duration in which masking occurs, critical interval varied with stimulus duration in such a way that the interval multiplied by the stimulus duration equals a constant. Critical stimulus duration and critical interval at threshold are shown to vary little under a variety of conditions. The effect of the random pattern stimulus is limited to the part of the visual field to which it is presented.     

Tuning perception: Visual working memory biases the quality of visual awareness

Studies of consciousness reveal that it is possible to manipulate subjective awareness of a visual stimulus. For example, items held in visual working memory (VWM) that match target features increase the speed with which the target reaches visual awareness. To examine the effect of VWM on perception, previous studies have mainly used coarse measures of awareness, such as present/absent or forced-choice judgments. These methods can reveal whether or not an individual has seen an item, but they do not provide information about the quality with which the item was seen. Using continuous report methods it has been shown that the fidelity of a perceived item can be affected by whether or not that item is masked. In the present study, we used an object-substitution masking task to examine whether items held in VWM would influence the quality with which a masked target reached awareness, or whether the threshold for awareness was instead affected by stimuli held in memory. We observed that targets matching the contents of VWM were recalled with greater precision compared to items that did not match the contents of VWM. Importantly, this effect occurred without affecting the likelihood of the target being perceived. These results suggest that VWM plays a greater role in modulating the fidelity of perceived representations than in lowering the overall threshold of awareness.     

Marginally perceptible outcome feedback, motor learning and implicit processes

Participants struck 500 golf balls to a concealed target. Outcome feedback was presented at the subjective or objective threshold of awareness of each participant or at a supraliminal threshold. Participants who received fully perceptible (supraliminal) feedback learned to strike the ball onto the target, as did participants who received feedback that was only marginally perceptible (subjective threshold). Participants who received feedback that was not perceptible (objective threshold) showed no learning. Upon transfer to a condition in which the target was unconcealed, performance increased in both the subjective and the objective threshold condition, but decreased in the supraliminal condition. In all three conditions, participants reported minimal declarative knowledge of their movements, suggesting that deliberate hypothesis testing about how best to move in order to perform the motor task successfully was disrupted by the impoverished disposition of the visual outcome feedback. It was concluded that sub-optimally perceptible visual feedback evokes implicit processes.     

NOTE ON SIMULTANEOUS DISCRIMINATION OF VISUAL ATTRIBUTES

van der H eijden A. H. C. Note on simultaneous discrimination of visual attributes. Scand. J. Psychol ., 1972, 13 , 71–72.—A tachistoscopically presented stimulus, provided it is above threshold, results in a visual image with a minimum duration of about 250 msec. In experiments on visual information processing, therefore, the results must be interpreted in terms of 'effective stimulus duration' (exposure time and duration of visual image) rather than exposure time alone.     

Autoshaping as a psychophysical paradigm: Absolute visual sensitivity in the pigeon

A classical conditioning procedure (autoshaping) was used to determine absolute visual threshold in the pigeon. This method provides the basis for a standardized visual psychophysical paradigm.     

Retroactive raising of a sensory threshold by a contralateral stimulus

In an experiment designed to extend Howarth and Treisman's recent observations on the lowering of the visual and auditory threshold produced by a warning stimulus, it has been found that the threshold to electrical stimulation of one forearm is raised by a similar stimulus on the other forearm. As in the earlier experiments the “warning” was effective if it came 100 millisec. before or after the threshold stimulus. The effect increased with increasing warning strength over the range of five near-threshold strengths used.

These results appear to be inconsistent with the explanation previously proposed to account for the retroactive lowering of threshold. This suggested that the warning was acting simply as a marker, reducing the subject's uncertainty as to when the stimulus was coming. The fact that the rise in threshold was also induced retroactively shows that some interaction must be occurring in the central processes concerned in perception, and that it cannot be explained in terms of attenuation of the afferent volley.     

Rate limits in sensorimotor synchronization with auditory and visual sequences: the synchronization threshold and the benefits and costs of interval subdivision

Synchronization of finger taps with an isochronous event sequence becomes difficult when the event rate exceeds a certain limit. In Experiment 1, the synchronization threshold was reached at interonset intervals (IOIs) above 100 ms with auditory tone sequences (in a 1:4 tapping task) but at IOIs above 400 ms with visual flash sequences (1:1 tapping). Using IOIs above those limits, the author investigated in Experiment 2 the reduction in the variability of asynchronies that tends to occur when the intervals between target events are subdivided by additional identical events (1:1 vs. 1:n tapping). The subdivision benefit was found to decrease with IOI duration and to turn into a cost at IOIs of 200-250 ms in auditory sequences and at IOIs of 450-500 ms in visual sequences. The auditory results are relevant to the limits of metrical subdivision and beat rate in music. The visual results demonstrate the remarkably weak rhythmicity of (nonmoving) visual stimuli.     

Retroactive contour enhancement: A new visual storage effect

A test stimulus (a visual form) which is below recognition threshold when flashed briefly against a steady background field can be raised to complete discriminability if the background field is terminated and replaced by darkness within about 100 msec of the test flash. There must therefore be an efficient storage process for the apparently “invisible” form. The phenomenon is shown to occur under a variety of conditions. It appears not to be a simple visual masking phenomenon. The tasks used are forced-choice, and the phenomenon provides a new demonstration of visual storage effects which previously have generally been reported only for supraliminal visual test stimuli.     

The effects of age on sensory thresholds and temporal gap detection in hearing, vision, and touch

Differences in sensory function between young (n 5 42, 18—31 years old) and older (n 5 137, 60—88 years old) adults were examined for auditory, visual, and tactile measures of threshold sensitivity and temporal acuity (gap-detection threshold). For all but one of the psychophysical measures (visual gap detection), multiple measures were obtained at different stimulus frequencies for each modality and task. This resulted in a total of 14 dependent measures, each based on four to six adaptive psychophysical estimates of 75% correct performance. In addition, all participants completed the Wechsler Adult Intelligence Scale (Wechsler, 1997). Mean data confirmed previously observed differences in performance between young and older adults for 13 of the 14 dependent measures (all but visual threshold at a flicker frequency of 4 Hz). Correlational and principalcomponents factor analyses performed on the data from the 137 older adults were generally consistent with task and modality independence of the psychophysical measures.     

Recognition of alphabetic characters during voluntary eye movements

In this paper we reconsider the question of vision during eye movements using a novel display procedure which guarantees that the eye was not stopped at any time during the eye movement. The results of our experiment lead us to conclude that true “saccadic suppression,” is a most elusive phenomenon. Furthermore, a brief analysis of the optics of the eye movement suggests that a substantial amount the elevation of visual threshold during eye movements can be attributed to simple retinal smear if one acknowledges the dominating importance of edge effects in visual threshold measurements.     

Assessing automaticity in the audiovisual integration of motion

This study examined the multisensory integration of visual and auditory motion information using a methodology designed to single out perceptual integration processes from post-perceptual influences. We assessed the threshold stimulus onset asynchrony (SOA) at which the relative directions (same vs. different) of simultaneously presented visual and auditory apparent motion streams could no longer be discriminated (Experiment 1). This threshold was higher than the upper threshold for direction discrimination (left vs. right) of each individual modality when presented in isolation (Experiment 2). The poorer performance observed in bimodal displays was interpreted as a consequence of automatic multisensory integration of motion information. Experiment 3 supported this interpretation by ruling out task differences as the explanation for the higher threshold in Experiment 1. Together these data provide empirical support for the view that multisensory integration of motion signals can occur at a perceptual level.