Duration Of Stimulus Presentation Research Articles

Electrophysiological and Psychophysical Studies of the Effects of the Duration of Presentation of Textures on Recognition Thresholds

The relationships between the number of correct responses, reaction time, and the main characteristics of visual evoked potentials (VEP) on the one hand, and the duration of stimulus presentation on the other were studied in tasks based on recognition of the dominant orientation of textures with different levels of ordering. Stimuli were presented for 30, 60, 130, 250, 500, and 1000 msec. The duration of presentation at which all subjects coped with the task was no greater than 130 msec in our experiments, and this coincided with the duration of stimulus presentation at which differences in EP depending on recognition task difficulty were seen. The first significant changes in EP depending on task difficulty developed 300 msec after the beginning of stimulus presentation and consisted of increases in the amplitude of the P300 component in response to the matrixes which were easiest to recognize. The coincidence of the recognition time thresholds and the appearance of differences in EP suggest that individual VEP waves may reflect activity associated with image recognition processes. The time characteristics of these processes were found to differ in different subjects. Two groups of observations were identified, with different time characteristics for perception and EP development.

The effect of stimulus duration and motor response in hemispatial neglect during a visual search task.

Patients with hemispatial neglect exhibit a myriad of profound deficits. A hallmark of this syndrome is the patients' absence of awareness of items located in their contralesional space. Many studies, however, have demonstrated that neglect patients exhibit some level of processing of these neglected items. It has been suggested that unconscious processing of neglected information may manifest as a fast denial. This theory of fast denial proposes that neglected stimuli are detected in the same way as non-neglected stimuli, but without overt awareness. We evaluated the fast denial theory by conducting two separate visual search task experiments, each differing by the duration of stimulus presentation. Specifically, in Experiment 1 each stimulus remained in the participants' visual field until a response was made. In Experiment 2 each stimulus was presented for only a brief duration. We further evaluated the fast denial theory by comparing verbal to motor task responses in each experiment. Overall, our results from both experiments and tasks showed no evidence for the presence of implicit knowledge of neglected stimuli. Instead, patients with neglect responded the same when they neglected stimuli as when they correctly reported stimulus absence. These findings thus cast doubt on the concept of the fast denial theory and its consequent implications for non-conscious processing. Importantly, our study demonstrated that the only behavior affected was during conscious detection of ipsilesional stimuli. Specifically, patients were slower to detect stimuli in Experiment 1 compared to Experiment 2, suggesting a duration effect occurred during conscious processing of information. Additionally, reaction time and accuracy were similar when reporting verbally versus motorically. These results provide new insights into the perceptual deficits associated with neglect and further support other work that falsifies the fast denial account of non-conscious processing in hemispatial visual neglect.

When perceptual time stands still: Long percept-memory in binocular rivalry

We have carried out binocular rivalry experiments with a large number of subjects to obtain high quality statistics on probability distribution of dominance duration (PDDD) for two cases where (a) the rival stimulus is continuously presented and (b) the rival stimulus is periodically removed, with stimulus-on and stimulus-off intervals Ton and Toff respectively. In the present study we have chosen to study the regime of relatively long stimulus-on time, i.e., Ton> 1s, where the stimulus presentation duration is significantly longer than the human reaction and recognition time. In the case of periodically removed stimulus, the total probability for percept reversal during each of the successive stimulus-on intervals Ton can be predicted using the PDDD for continuous viewing. More importantly, this total probability for percept reversal during any stimulus-on interval is independent of the length Toff of the preceding blank time, which can be quite long. We argue that this suggests that, in the regime of long Ton and Toff considered here, the variables representing the perceptual state do not change significantly during long blank intervals. We discuss that these findings impose challenges to theoretical models which aim at describing visual perception.

The effect of poser race on the happy categorization advantage depends on stimulus type, set size, and presentation duration.

The question as to whether poser race affects the happy categorization advantage, the faster categorization of happy than of negative emotional expressions, has been answered inconsistently. Hugenberg (2005) found the happy categorization advantage only for own race faces whereas faster categorization of angry expressions was evident for other race faces. Kubota and Ito (2007) found a happy categorization advantage for both own race and other race faces. These results have vastly different implications for understanding the influence of race cues on the processing of emotional expressions. The current study replicates the results of both prior studies and indicates that face type (computer-generated vs. photographic), presentation duration, and especially stimulus set size influence the happy categorization advantage as well as the moderating effect of poser race.

Artistic representations: Clues to efficient coding in human vision

In what ways is mammalian vision--and in particular, human vision--efficiently adapted to its ecology? We suggest that human visual artwork, which is made for the human eye, holds clues that could help answer this question. Paintings are readily perceived as representations of natural objects and scenes, yet statistical relationships between natural images and paintings are nontrivial. Although spatial frequency content is generally similar for art and natural images, paintings cannot reproduce the dynamic range of luminance in scenes. Through a variety of image manipulations designed to alter image intensity distributions and spatial contrast, we here investigate the notion that artists' representational strategies can efficiently capture salient features of natural images, and in particular, of faces. We report that humans perform near flawless discrimination of faces and nonfaces in both paintings and natural images, even for stimulus presentation durations of 12 ms. In addition, contrast negation and up-down inversion have minimal to no effect on performance for both image types, whereas 1/f noise addition significantly affects discrimination performance for art more than for natural images. Together, these results suggest artists create representations that are highly efficient for transmitting perceptual information to the human brain.

Nonlinear estimation of neural processing time from BOLD signal with application to decision-making

The extraction of information about neural activity timing from BOLD signal is a challenging task as the shape of the BOLD curve does not directly reflect the temporal characteristics of electrical activity of neurons. In this work, we introduce the concept of neural processing time (NPT) as a parameter of the biophysical model of the hemodynamic response function (HRF). Through this new concept we aim to infer more accurately the duration of neuronal response from the highly nonlinear BOLD effect. The face validity and applicability of the concept of NPT are evaluated through simulations and analysis of experimental time series. The results of both simulation and application were compared with summary measures of HRF shape. The experiment that was analyzed consisted of a decision-making paradigm with simultaneous emotional distracters. We hypothesize that the NPT in primary sensory areas, like the fusiform gyrus, is approximately the stimulus presentation duration. On the other hand, in areas related to processing of an emotional distracter, the NPT should depend on the experimental condition. As predicted, the NPT in fusiform gyrus is close to the stimulus duration and the NPT in dorsal anterior cingulate gyrus depends on the presence of an emotional distracter. Interestingly, the NPT in right but not left dorsal lateral prefrontal cortex depends on the stimulus emotional content. The summary measures of HRF obtained by a standard approach did not detect the variations observed in the NPT.

A meta-analysis of the magnitude of biased attention in depression

In this quantitative review, we examined the magnitude of attentional biases to negative stimuli in depression. Results from 29 empirical studies examining emotional Stroop or dot probe results in depressed participants (clinical depression, nonclinical dysphoria, and subjects undergoing depressive mood induction) were examined. Studies using the emotional Stroop task yielded marginally significant evidence of a difference between depressed and nondepressed samples, whereas those using the dot probe task showed significant differences between groups (d = 0.52). We found no evidence for significant moderation of these effects by age, sex, type of depressed sample, year of publication, stimulus presentation duration, or type of stimuli (verbal or nonverbal), although statistical power for these tests was limited. These results support the existence of biased attention to negative information in depression.

Time-course of attentional bias for threat-related cues in patients with chronic daily headache–tension type: Evidence for the role of anger

This study investigated the role of anger in attentional bias for linguistic threat-related stimuli in individuals with chronic daily headache (CDH) tension type and healthy controls. Attentional bias was assessed using a visual probe task which presented pain-related (sensory and affective), social threat, anger-related, and neutral words at two exposure duration conditions: 500 ms and 1250 ms. Compared to healthy controls, individuals with CDH showed significantly greater attentional bias towards pain-related words at 1250 ms, indicating a bias in maintained attention to pain cues in this group. No significant differences between groups were found in attentional bias scores at the shorter stimulus duration of 500 ms. No significant differences between groups were found in attentional bias scores to social threat and anger-related words at either stimulus presentation duration. When compared to 0, in all group and duration combinations there was significant positive bias towards anger. Across the whole sample, pain bias scores at 1250 ms were significantly associated with anger out, whilst anger bias scores at both 500 ms and 1250 ms correlated significantly with trait anger. The results of the present investigation support the content-specificity hypothesis, according to which attentional bias in patients with chronic pain is shown only towards pain-related cues. Moreover, the current pattern of results highlights the importance of exploring further the role of anger in the aetiology and maintenance of chronic pain in general, and CDH tension type in particular.

State-Dependent Effects of Stimulus Presentation Duration on the Temporal Dynamics of Neural Responses in the Inferotemporal Cortex of Macaque Monkeys

During natural vision, stimuli are viewed for different durations as the state of brain activity changes over time. Here we studied the effects of stimulus presentation duration on cell responses (n=259) in three subdivisions of the inferotemporal (IT) cortex of fixating macaque monkeys as neural baseline firing rates varied over the course of recording. First, cell responses to the presentation of 120 images were tested, and four images that elicited significant responses with various degrees of effectiveness were selected for further study. Then the four selected images were presented to the monkeys for five different presentation durations (18, 70, 140, 210, and 350 ms). We found that depending on the magnitude of neural baseline activity, stimulus presentation duration affected the response properties and efficiency of neural information processing in the IT cortex. Short stimulus presentation durations elicited phasic responses consisting of rhythmic activation and inactivation, which conveyed a lower amount of stimulus information, particularly following higher baseline firing rates. Longer presentation durations elicited a sustained pattern of response and carried a greater amount of information, particularly at lower baseline firing rates. Finally, a significantly higher proportion of cells in the posterior IT compared with the anterior IT had a tendency to have high baseline activity, recruit stronger phasic responses and convey less information. It is plausible that during natural vision, as stimuli with various exposure durations affect the visual system, top-down influence or competition within local neural networks differentially influences the function of IT cells by changing their baseline activity.

Design of a New Somatosensory Stimulus Delivery Device for Measuring Laryngeal Mechanosensory Detection Thresholds in Humans

Laryngeal control is essential for airway protection, breathing, deglutition, speech, and voice. Unfortunately, integration of laryngeal sensory assessment in research and clinical practice is limited by technical and practical limitations of commercially available technology. A commercial device is available, but reported limitations include procedural complexity requiring two or three individuals to operate, limited stimulus dynamic range, device generated noise, and questionable stimulus reproducibility. The objective of this study was to design a new laryngeal somatosensory stimulus delivery device that provides direct, reliable control over the timing, duration, and dynamic range of stimulus presentation, and test the device in individuals who may manifest a laryngeal sensory deficit. The new device operates silently and has more than four times greater stimulus dynamic range than the commercial device. Testing with the new device revealed laryngeal mechanosensory detection thresholds in an individual with Parkinson's disease that were seven times higher than those of healthy controls. These data would have otherwise gone undetected due to limited stimulus dynamic range in the commercial device. The new design resulted in a new assessment instrument that is simple to use for routine clinical assessment, yet sufficiently versatile for integration within rigorous clinical research protocols.

Human single-neuron responses at the threshold of conscious recognition

We studied the responses of single neurons in the human medial temporal lobe while subjects viewed familiar faces, animals, and landmarks. By progressively shortening the duration of stimulus presentation, coupled with backward masking, we show two striking properties of these neurons. (i) Their responses are not statistically different for the 33-ms, 66-ms, and 132-ms stimulus durations, and only for the 264-ms presentations there is a significantly higher firing. (ii) These responses follow conscious perception, as indicated by the subjects' recognition report. Remarkably, when recognized, a single snapshot as brief as 33 ms was sufficient to trigger strong single-unit responses far outlasting stimulus presentation. These results suggest that neurons in the medial temporal lobe can reflect conscious recognition by "all-or-none" responses.

Simultaneously measured behavioral and electrophysiological hearing thresholds in a bottlenose dolphin (Tursiops truncatus)

Dolphin auditory thresholds obtained via evoked potential audiometry may deviate from behavioral estimates by 20 dB or more. Differences in the sound source, stimulus presentation method, wave form, and duration may partially explain these discrepancies. To determine the agreement between behavioral and auditory evoked potential (AEP) threshold estimates when these parameters are held constant, behavioral and AEP hearing tests were simultaneously conducted in a bottlenose dolphin. Measurements were made in-air, using sinusoidal amplitude-modulated tones continuously projected via a transducer coupled to the pan region of the dolphin's lower jaw. Tone trials were presented using the method of constant stimuli. Behavioral thresholds were estimated using a 50% correct detection. AEP thresholds were based on the envelope following response and 50% correct detection. Differences between AEP and behavioral thresholds were within +/-5 dB, except at 10 kHz (12 dB), 20 kHz (8 dB), 30 kHz (7 dB), and 150 kHz (24 dB). In general, behavioral thresholds were slightly lower, though this trend was not significant. The results demonstrate that when the test environment, sound source, stimulus wave form, duration, presentation method, and analysis are consistent, the magnitude of the differences between AEP and behavioral thresholds is substantially reduced.

Stimuli of varying spatial scale induce gamma activity with distinct temporal characteristics in human visual cortex

Gamma activity to stationary grating stimuli was studied non-invasively using MEG recordings in humans. Using a spatial filtering technique, we localized gamma activity to primary visual cortex. We tested the hypothesis that spatial frequency properties of visual stimuli may be related to the temporal frequency characteristics of the associated cortical responses. We devised a method to assess temporal frequency differences between stimulus-related responses that typically exhibit complex spectral shapes. We applied this methodology to either single-trial (induced) or time-averaged (evoked) responses in four frequency ranges (0–40, 20–60, 40–80 and 60–100 Hz) and two time windows (either the entire duration of stimulus presentation or the first second following stimulus onset). Our results suggest that stimuli of varying spatial frequency induce responses that exhibit significantly different temporal frequency characteristics. These effects were particularly accentuated for induced responses in the classical gamma frequency band (20–60 Hz) analyzed over the entire duration of stimulus presentation. Strikingly, examining the first second of the responses following stimulus onset resulted in significant loss in stimulus specificity, suggesting that late signal components contain functionally relevant information. These findings advocate a functional role of gamma activity in sensory representation. We suggest that stimulus specific frequency characteristics of MEG signals can be mapped to processes of neuronal synchronization within the framework of coupled dynamical systems.

Visual search and eye movements in patients with chronic solvent-induced toxic encephalopathy

Various aspects of visual perception have been found to be impaired in patients with occupational chronic solvent-induced toxic encephalopathy (CSE). The purpose of the study was to characterise the changes in eye movements and visual search performance in CSE patients. We measured eye movements of 13 CSE patients and 22 healthy controls during dynamic visual search task by using a fast video eye tracker. The task was to search for and identify a target letter among numerals presented in a rectangular stimulus matrix (3 × 3–10 × 10 items). Threshold search time, i.e. the duration of stimulus presentation required for identifying the target with a given probability was determined by using a psychophysical staircase method. The visual search times of the CSE patients were clearly longer, and they needed considerably more eye fixations than healthy controls to find the target. Thus, their reduced performance in this task was mainly related to the reduction in the number of items which could be processed during a single eye fixation ( perceptual span). This reduction probably reflects a limited capacity of visual attention, since visual acuity, contrast sensitivity, and the oculomotor saccade velocity were found to be normal. The results suggest that motor slowness or low-level visual factors do not explain the poor performance of CSE patients in visual search tasks. The results are also discussed with respect to the effects of education, and compared to the performance in the widely used neuropsychological Trail Making Test, which uses similar stimuli and requires visual search.

Object-Selective Cortex Exhibits Performance-Independent Repetition Suppression

Object-selective cortical regions exhibit a decreased response when an object stimulus is repeated [repetition suppression (RS)]. RS is often associated with priming: reduced response times and increased accuracy for repeated stimuli. It is unknown whether RS reflects stimulus-specific repetition, the associated changes in response time, or the combination of the two. To address this question, we performed a rapid event-related functional MRI (fMRI) study in which we measured BOLD signal in object-selective cortex, as well as object recognition performance, while we manipulated stimulus repetition. Our design allowed us to examine separately the roles of response time and repetition in explaining RS. We found that repetition played a robust role in explaining RS: repeated trials produced weaker BOLD responses than nonrepeated trials, even when comparing trials with matched response times. In contrast, response time played a weak role in explaining RS when repetition was controlled for: it explained BOLD responses only for one region of interest (ROI) and one experimental condition. Thus repetition suppression seems to be mostly driven by repetition rather than performance changes. We further examined whether RS reflects processes occurring at the same time as recognition or after recognition by manipulating stimulus presentation duration. In one experiment, durations were longer than required for recognition (2 s), whereas in a second experiment, durations were close to the minimum time required for recognition (85-101 ms). We found significant RS for brief presentations (albeit with a reduced magnitude), which again persisted when controlling for performance. This suggests a substantial amount of RS occurs during recognition.

Rapid Visual Information Processing in Schizophrenic Patients: The Impact of Cognitive Load and Duration of Stimulus Presentation

The inability to sustain attention has been proposed as a core deficit in schizophrenia. The Continuous Performance Task (AX-CPT) and the Rapid Visual Information Processing Task (RVP) are widely used neuropsychological tasks to measure sustained attention. The RVP displays numbers as stimuli, whereas the AX-CPT uses letters. Ten patients with chronic schizophrenia and 18 healthy control subjects were studied using four different versions of the RVP. The versions differed with regard to stimulus presentation time (600 vs. 1,200 ms) and the number of target sequences to be memorized: either one sequence (low cognitive load) or two sequences (high cognitive load). Schizophrenic patients showed a reduced number of hits only on the task version with 600 ms stimulus duration coupled with high cognitive load. The combination of high cognitive load and short stimulus duration created a critical performance breaking point for schizophrenic patients. This finding supports the hypothesis that patients have an impaired ability to coactivate different cognitive performances; thus the results favor the theory of impaired functional connectivity in schizophrenia.

Category-Specific Effects in Object Identification: What is “Normal”?

Previous research on category-specific effects in subjects with intact brains, have found a disadvantage for the identification of natural objects compared to artefacts. This has been taken to support the explanation that natural object deficits in brain-damaged subjects are nothing more than an exaggeration of a “normal” tendency. More recent investigations have, however, uncovered the opposite normal tendency, an advantage for natural objects (Gerlach, 2001; Laws and Neve, 1999). The present study investigated the possible causes of this discrepancy. Three experiments revealed category-specific disadvantages for natural objects in normal subjects despite using stimulus materials rigorously balanced for a) concept familiarity, b) visual complexity, c) name frequency and d) name length. Furthermore, it was found that the very same set of stimulus materials could lead to natural object advantages as well as natural object disadvantages, depending on whether trials in a matching paradigm were positive or negative. In a naming paradigm, there was no natural object disadvantage when stimulus presentation durations were short. The discrepancy present in the literature can be solved by an account emphasising perceptual strategies instead of invoking a lack of adequate experimental control in the previous studies.

How many faces can be processed during a single eye fixation?

The purpose of our study was to estimate the perceptual span for facial information: how many faces can be processed during a single eye fixation. We used a visual-search task, in which the targets and distractors were facial photographs. The task of the observer was to search for and identify a target face in an array of faces. We measured the time needed for one search--threshold search time--by using a multiple-alternative staircase method. The threshold represents the duration of stimulus presentation at which the probability of correct responses was 79%. The array size was varied from 2 x 2 to 8 x 8 faces. Simultaneously with the performance measurements we measured eye movements with a video eye tracker. We found that threshold search time increased with increasing set size nearly linearly. The number of fixations also increased linearly from unity at the smallest set size to about fifteen at the largest set size. The result of 2 x 2 faces during a single fixation gave an estimate of 4 faces for the perceptual span. If, on average, only half of the elements had to be scanned for finding the target, 15 fixations at the largest set size (8 x 8) gave another estimate of 2.13 faces. The mean fixation duration was around 200 ms. Thus, the results suggest that 2-4 faces can be processed during one fixation of about 200 ms.

Display quality and the speed of visual letter search

Previously it has been suggested that visual search tasks can be used to evaluate the perceptual quality of display devices with respect to their ability to convey alphanumeric information. The purpose of the present study was to examine how character size and contrast used in a visual search test affects its sensitivity to differences in the quality of display devices. The task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numerals. Threshold search time, that is, the duration of stimulus presentation required for search that is successful with a given probability, was determined by using a multiple-alternative staircase method. Eye movements were recorded simultaneously by using a fast video eye tracker. Threshold search times were measured as a function of character size at two contrast levels using a CRT and an LCD display. For all experimental conditions, threshold search time decreased with increasing letter size. This was accompanied with a decrease in the number of eye fixations per search as well as a decrease of fixation duration. At high contrast ( C Michelson≈1), no statistically significant difference was found between the two displays. However, at the lower contrast used ( C Michelson≈0.2) and at small character sizes, threshold search times for the CRT display were clearly longer and the number of fixations per search was higher than for the LCD display. In conclusion, visual letter search is a more sensitive method for display evaluation at small contrasts and with small character sizes.

Effect of stimulus contrast on performance and eye movements in visual search

According to the visual span control hypothesis, eye movements are controlled in relation to the size of visual span. In reading, the decrease of contrast reduces visual span, saccade sizes, and reading speed. The purpose of the present study is to determine how stimulus contrast affects the speed of two-dimensional visual search and how changes in eye movements and visual span could explain changes in performance. The task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numerals. Threshold search time, i.e. the duration of stimulus presentation required for search that is successful with a given probability, was determined by using a multiple-alternative staircase method. Eye movements were recorded simultaneously by using a video eye tracker. Four different set sizes (the sizes of stimulus array) (3×3–10×10), and five different contrasts (0.0186–0.412) were used. At all set sizes, threshold search time decreased with increasing contrast. Also the average number of fixations per search decreased with increasing contrast. At the smallest set size (3×3), only one fixation was needed except at the lowest contrast. Average fixation duration decreased and saccade amplitudes increased slightly with increasing contrast. The reduction of the number of fixations with increasing contrast suggests that visual span, i.e. the area from which information can be collected at one fixation, increases with increasing contrast. The reduction of the number of fixations together with reduced fixation duration result in reduced search times when contrast increases.