Differential Latencies Research Articles

Modeling crowding based on interactions between sustained and transient channels and differential latencies

Modeling crowding based on interactions between sustained and transient channels and differential latencies

Differential Latencies Sculpt the Time Course of Contextual Effects on Spatial Perception.

The ability to judge an object's orientation with respect to gravitational vertical relies on an egocentric reference frame that is maintained using not only vestibular cues but also contextual cues provided in the visual scene. Although much is known about how static contextual cues are incorporated into the egocentric reference frame, it is also important to understand how changes in these cues affect perception, since we move about in a world that is itself dynamic. To explore these temporal factors, we used a variant of the rod-and-frame illusion, in which participants indicated the perceived orientation of a briefly flashed rod (5-msec duration) presented before or after the onset of a tilted frame. The frame was found to bias the perceived orientation of rods presented as much as 185 msec before frame onset. To explain this postdictive effect, we propose a differential latency model, where the latency of the orientation judgment is greater than the latency of the contextual cues' initial impact on the egocentric reference frame. In a subsequent test of this model, we decreased the luminance of the rod, which is known to increase visual afferent delays and slow decision processes. This further slowing of the orientation judgment caused the frame-induced bias to affect the perceived orientation of rods presented even further in advance of the frame. These findings indicate that the brain fails to compensate for a mismatch between the timing of orientation judgments and the incorporation of visual cues into the egocentric reference frame.

Decoupling of Early V5 Motion Processing from Visual Awareness: A Matter of Velocity as Revealed by Transcranial Magnetic Stimulation.

Motion information can reach V5/MT through two parallel routes: one conveying information at early latencies through a direct subcortical route and the other reaching V5 later via recurrent projections through V1. Here, we tested the hypothesis that input via the faster direct pathway depends on motion characteristics. To this end, we presented motion stimuli to healthy human observers at different velocities (4.4°/sec vs. 23°/sec) with static stimuli as controls while applying transcranial magnetic stimulation (TMS) pulses over V5 or V1. We probed for TMS interference with objective (two-alternative forced choice [2AFC]) and subjective (awareness) measures of motion processing at six TMS delays from stimulus onset (poststimulus window covered: ∼27-160 msec). Our results for V5-TMS showed earlier interference with objective performance for fast motion (53.3 msec) than slow motion (80 msec) stimuli. Importantly, TMS-induced decreases in objective measures of motion processing did correlate with decreases in subjective measures for slow but not fast motion stimuli. Moreover, V1-TMS induced a temporally unspecific interference with visual processing as it impaired the processing of both motion and static stimuli at the same delays. These results are in accordance with fast moving stimuli reaching V5 through a different route than slow moving stimuli. The differential latencies and coupling to awareness suggest distinct involvement of a direct (i.e., colliculo-extrastriate) connection bypassing V1 depending on stimulus velocity (fast vs. slow). Implication of a direct pathway in the early processing of fast motion may have evolved through its behavioral relevance.

On vs. off-object probes produce differential ERPs and reversal latencies in binocular rivalry

On vs. off-object probes produce differential ERPs and reversal latencies in binocular rivalry

Short-distance sensory stimulation technique in the early diagnosis of carpal tunnel syndrome

Abstract Aim. Normal results obtained from nerve conduction studies do not exclude the diagnosis of carpal tunnel syndrome (CTS). We intended to increase diagnostic sensitivity of nerve conduction studies in the early stage CTS by stimulating shorter palm-wrist segment, and excluding distal region outside the entrapment site of the median nerve which is unaffected from pathologic changes. Methods. In this prospective study, 41 patients (66 hands) with clinically diagnosed CTS with normal conventional electrophysiologic examinations were stimulated with electrodes placed at 8, 7, 6, 5, 4 cm from the distal wrist crease (DWC) on the palm-wrist segment, and the conduction velocities, latencies, and the differential latencies (conduction delay) were compared with those of 34 patients (68 hands) in the control group. Results. Conduction delay recorded between 4-5, 5-6, 6-7, 7-8 cm. away from DWC of both groups was statistically insignificant (p>0.1), while the conduction velocities and the latencies obtained from the electrodes placed on 4, 5, 6, 7, and 8 cm away from DWC differed statistically significantly between two groups (p 0.1); 4, 5, 6, 7, 8. cm.’lerdeki hiz, latans degerleri her iki grup arasinda istatistiksel olarak anlamli bulunmustur (p<0.001). Sonuc. KTS tanisini dogrulamak icin yapilan elektrofizyolojik incelemede, avucici-bilek segmentinde, mesafenin daha kisa tutulup, uyarimin DBC’nin 4 ve/veya 5 cm distalinden yapilmasi, karpal tuneldeki hafif ve lokalize iletim gecikmesini tespit etmede yeterlidir. Iletim hizi normal olan distal segmentin hafifletici etkisinin ortadan kalkmasiyla duyarlilik %92,4’e yukselmistir. Anahtar sozcukler: Karpal tunel sendromu, sinir ileti calismalari, avucici-bilek iletimi, kisa mesafe stimulasyon

Latencies Shorter than 3.5 ms After Vagus Nerve Stimulation Signify a Nonrecurrent Inferior Laryngeal Nerve Before Dissection

Quantitative electromyographic signals recorded after vagus nerve stimulation during intraoperative neuromonitoring (IONM) were analyzed for their clinical usefulness to identify and track a nonrecurrent inferior laryngeal nerve (NRLN) before dissection. A NRLN is anatomically shorter than a recurrent inferior laryngeal nerve (RLN). This disparity should cause differential latencies after vagus nerve stimulation during IONM, which may aid in distinguishing a NRLN from a RLN. Failure to identify a NRLN early on entails a great risk of nerve injury. Included in this IONM case-control study were 18 cases with a NRLN and 36 controls with RLN anatomy matched for gender, age, body size, and underlying thyroid and parathyroid disease. All 18 NRLN were found in the right neck only. Cases with a NRLN had significantly shorter latencies than controls (medians of 2.7 vs. 4.6 ms; P < 0.001) but comparable amplitude and duration after stimulation of the right vagus nerve. With a latency threshold of <3.5 ms, sensitivity, specificity, positive and negative predictive value, and accuracy, respectively, were 100%, 94%, 100%, 97%, and 98% for diagnosis of a NRLN. A latency threshold of 3.5 ms after ipsilateral vagus nerve stimulation during IONM was able to discriminate well between a NRLN and a RLN in adults, helping avoid injury to the aberrant nerve. Additional studies should explore latency thresholds in children and adolescents who have shorter inferior laryngeal nerves and conceivably shorter latencies than adults.

Substitutional mediation in matching to sample with words: comparison between children and adults

Children and adults were trained with three procedures of conditional discrimina­tion in a computerized matching to sample task with words, in order to assess the level of mediation generated by them. Matching was done on the basis of color, size of letters, semantic equivalence and semantic inclusion. Three procedures were used: choice of comparative instances (Scom), choice of relations (Ssor) and choice of sample instances (Ss); subjects passed through all of them according to a latin square designo Tests of concurrent choice of Ssor, Scom and Ss were used for the transference phases, before, during and after training. In general all subjects scored higher with synonymy; children scored low both in acquisition and intramodal transference, while adults showed high scores for semantic matches; extramodal transference was null for children and high for adults in synonyms. Choice of relations produced the highest scores for physical matches with both children and adults. Order of exposure did not affect children's performance in a significant way, while adults scored slight1y better with initial exposure to choice of comparative instances. Children preferred physical matches, in spite of rating higher for synonyms, on the other hand adults preferred synonyms. Latencies for synonyms were the shortes in adults; while children did not show differential latencies. Types of me­diation are discussed in terms of differences among procedures, differences in level of detachment implied in learning physical and semantical matches and differences in verbal competence.

Dynamics of majority rule with differential latencies

We investigate the dynamics of the majority-rule opinion formation model when voters experience differential latencies. With this extension, voters that just adopted an opinion go into a latent state during which they are excluded from the opinion formation process. The duration of the latent state depends on the opinion adopted by the voter. This leads to a bias toward consensus on the opinion that is associated with the shorter latency. We determine the exit probability and time to consensus for systems of N voters. Additionally, we derive an asymptotic characterization of the time to consensus by means of a continuum model.

Simple differential latencies modulate, but do not cause the flash-lag effect

When a brief static flash is presented in physical alignment with a moving target, the position of the flash can seem to lag behind that of the moving target. Various explanations exist. One of the most popular is the differential latency hypothesis. This assumes that neural latencies for moving stimuli are shorter than those for static stimuli. Accordingly, the flash lag would occur because perception is temporally fragmented, with moving stimuli seen before static. To test this, observers were asked to make different judgments concerning the same stimulus. Observers either judged if color changes in moving and static stimulus sections were synchronous, or whether the different stimulus sections were aligned at the time of a color change. If the flash-lag were driven by a simple differential latency, we would expect both judgments to be marked by a temporal advantage for moving stimuli. Our results suggest the contrary, as only the later judgment was marked by a flash-lag effect. The apparent timing of moving and static color changes was veridical. However, when we introduced a systematic differential latency, by modulating image contrast, both judgments were affected. Our data therefore suggest that a simple differential can modulate flash-lag type effects, but they do not cause the phenomenon.

The correlation-based model: An alternative system for analyzing ERP data in cognitive research

This study is focused on the development of a model for analyzing electrophysiological data (EEG) utilizing the evoked potentials (ERP) method used in cognitive research. The aim of the model is to overcome several limitations arising from traditional methods of ERP analysis. The model was tested for its ability to distinguish between dyslexic and regular readers. ERP data collected during a typical experiment contain a large amount of information that is not utilized during data analysis. For instance, it is acceptable to define a component such as the P300 according to the peak of a wave based on a few electrodes. Furthermore, this is often accomplished based on the researcher's subjective impression. Information such as the pattern of the wave, its width, rate of ascent, rate of descent, and the impact of the stimulus that evoked it over the entire scalp, is left out. In contrast, the modeling method proposed here considers all available information, utilizing a precise algorithm that allows fully automated analysis. The method produces a typical profile for a given type of subject and can determine for each new subject his/her similarity to that type. The basic idea behind the model is that two subjects exposed to the same task would share certain similarities in their electrophysiological data. However, the latency of this shared similarity might differ from person to person. It is thus possible to take the data from one subject and systematically seek the point of maximal similarity across all electrodes. Consequently, the data matrix of subject A in the area of P300 (e.g., all information on all electrodes between 250 and 350 ms) will be correlated with the data of subject B of the same width, i.e., 100 ms running from 200 ms throughout 400 ms. The correlation between the two matrices is expected to rise as the area of similarity gets closer, and descend once past that point. The size of the maximal correlation indicates the similarity between the two subjects, and its location in time indicates differential latencies. The averaging of data across subjects should be carried out at the points of maximal similarity. In order to demonstrate the power of the method, this study constructed two separate models for a dyslexic and regular reader, respectively. The models were based on ERP data recorded during a lexical decision task. The similarity of each subject to both models was calculated. This method correctly classified 68% of subjects. In addition, the model was able to detect sub-groups within each diagnostic category with distinct behavioral patterns.

Comparison of differential neuronal responsiveness for different regions of the prefrontal cortex in a conditional visual discrimination task

To investigate neuronal processing during monkeys' performance of a visual conditional discrimination task, recordings were made from four areas of prefrontal cortex (ventromedial, orbitofrontal, dorsolateral and anterior cingulate) where lesions have been shown to produce impairment of such tasks. Of 1911 recorded neurons, 573 (31%) responded to elements of the task. This proportion was less than the 50% previously reported as responsive in temporal cortex under the same conditions, suggesting sparser encoding in prefrontal than temporal cortex. Of the responsive prefrontal neurons, 165 (29%) responded differently on the different types of trial, so signalling various types of information relevant to task performance and cognition. In line with recent lesion findings, in the dorsolateral region the incidence of such differentially responsive neurons was only an eighth that in the other regions. The relatively high incidence of neuronal responses that encoded a potential instruction cue rather than specific individual stimulus arrangements was consistent with the animals solving the task by using such information, though other neuronal responses could have enabled the task to have been solved by rote learning. Compared to temporal neurons, prefrontal responses more frequently coded information relating to the planned behavioural response rather than perceptual aspects of the task. Population differential response latencies were long (> approximately 225 ms) in prefrontal cortex. A comparison of such differential latencies between temporal and prefrontal cortex indicated that potential information flow was likely to be primarily from temporal to prefrontal cortex rather than vice versa.

Attention bias to faces in Asperger Syndrome: a pictorial emotion Stroop study

Emotional Stroop tasks have shown attention biases of clinical populations towards stimuli related to their condition. Asperger Syndrome (AS) is a neuropsychiatric condition with social and communication deficits, repetitive behaviours and narrow interests. Social deficits are particularly striking, including difficulties in understanding others. We investigated colour-naming latencies of adults with and without AS to name colours of pictures containing angry facial expressions, neutral expressions or non-social objects. We tested three hypotheses: whether (1) controls show longer colour-naming latencies for angry versus neutral facial expressions with male actors, (2) people with AS show differential latencies across picture types, and (3) differential response latencies persist when photographs contain females. Controls had longer latencies to pictures of male faces with angry compared to neutral expressions. The AS group did not show longer latencies to angry versus neutral expressions in male faces, instead showing slower latencies to pictures containing any facial expression compared to objects. When pictures contained females, controls no longer showed longer latencies for angry versus neutral expressions. However, the AS group still showed longer latencies to all facial picture types, compared to objects, providing further evidence that faces produce interference effects for this clinical group. The pictorial emotional Stroop paradigm reveals normal attention biases towards threatening emotional faces. The AS group showed Stroop interference effects to all facial stimuli regardless of expression or sex, suggesting that faces cause disproportionate interference in AS.

Point: The muscle metaboreflex does restore blood flow to contracting muscles

Imposed reductions in oxygen delivery to active skeletal muscle during dynamic exercise in conscious dogs evoke a powerful pressor response, termed the muscle metaboreflex. During submaximal work rates, the major mechanism used by this reflex is to increase cardiac output (CO), which generates a

Differential latencies and the dynamics of the position computation process for moving targets, assessed with the flash-lag effect

To investigate the dynamics of the position computation process for a moving object in human vision, we measured the response to a continuous change in position at a constant velocity (ramp-response) using the flash-lag illusion. In this illusion, flashed and moving objects appear spatially offset when their retinal images are physically aligned. The steady-state phase of the ramp-response was probed using the “continuous-motion” (CM) paradigm, in which the motion of the moving object starts long before the occurrence of the flash. To probe the transient phase of the ramp-response, we used the “flash-initiated cycle” (FIC) paradigm, in which the motion of the moving object starts within a short time window around the presentation of the flash. The sampling instant of the ramp-response was varied systematically by changing the luminance or the presentation time of the flashed stimulus. We found that the perceived flash misalignments in the FIC and CM paradigms were approximately equal when sampling of the ramp-response occurred after a relatively long delay from the onset of motion and, were significantly different when sampling of the ramp-response occurred at a relatively short delay. The systematic variations in the perceived misalignment between the moving and flashed stimuli as a function of stimulus parameters are compared to the predictions of our differential latency and to alternative models of position computation.

Differential latencies and the dynamics of the position computation process for moving targets, assessed with the flash-lag effect

To investigate the dynamics of the position computation process for a moving object in human vision, we measured the response to a continuous change in position at a constant velocity (ramp-response) using the flash-lag illusion. In this illusion, flashed and moving objects appear spatially offset when their retinal images are physically aligned. The steady-state phase of the ramp-response was probed using the “continuous-motion” (CM) paradigm, in which the motion of the moving object starts long before the occurrence of the flash. To probe the transient phase of the ramp-response, we used the “flash-initiated cycle” (FIC) paradigm, in which the motion of the moving object starts within a short time window around the presentation of the flash. The sampling instant of the ramp-response was varied systematically by changing the luminance or the presentation time of the flashed stimulus. We found that the perceived flash misalignments in the FIC and CM paradigms were approximately equal when sampling of the ramp-response occurred after a relatively long delay from the onset of motion and, were significantly different when sampling of the ramp-response occurred at a relatively short delay. The systematic variations in the perceived misalignment between the moving and flashed stimuli as a function of stimulus parameters are compared to the predictions of our differential latency and to alternative models of position computation.

Latency differences and the flash-lag effect

The tendency for briefly flashed stimuli to appear to lag behind the spatial position of physically aligned moving stimuli is known as the flash-lag effect. Possibly the simplest explanation for this phenomenon is that transient stimuli are processed more slowly than moving stimuli. We tested this proposal using a task based upon the simultaneous tilt illusion. When an oriented stimulus is surrounded by another oriented stimulus, the inner stimulus can appear to be rotated away from the orientation of the surround. By flashing central static sinewave gratings at specific phases of an annular gratings rotation cycle, we were able to determine the temporal dependence of the tilt illusion. Our results suggest a small, ∼20 ms, processing advantage for the rotating stimulus relative to the flashed stimulus. Such a small advantage, if due to differential latencies, is insufficient to account for the flash-lag effect.

The attentional modulation of the flash-lag effect.

If a dot is flashed in perfect alignment with a pair of dots rotating around the visual fixation point, most observers perceive the rotating dots as being ahead of the flashing dot (flash-lag effect). This perceptual effect has been interpreted to result from the perceptual extrapolation of the moving dots, the differential visual latencies between flashing and moving stimuli, as well as the modulation of attentional mechanisms. Here we attempted to uncouple the attentional effects brought about by the spatial predictability of the flashing dot from the sensory effects dependent on its visual eccentricity. The stimulus was a pair of dots rotating clockwise around the fixation point. Another dot was flashed at either the upper right or the lower left of the visual field according to three separate blocked situations: fixed, alternate and random positions. Twenty-four participants had to judge, in all three situations, the location of the rotating dots in relation to the imaginary line connecting the flashing dot and the fixation point at the moment the dot was flashed. The flash-lag effect was observed in all three situations, and a clear influence of the spatial predictability of the flashing dot on the magnitude of the perceptual phenomenon was revealed, independently of sensory effects related to the eccentricity of the stimulus in the visual field. These findings are consistent with our proposal that, in addition to sensory factors, the attentional set modulates the magnitude of the differential latencies that give rise to the flash-lag phenomenon.

Detecting Latency Differences in Event-Related BOLD Responses: Application to Words versus Nonwords and Initial versus Repeated Face Presentations

We introduce a new method for detecting differences in the latency of blood oxygenation level-dependent (BOLD) responses to brief events within the context of the General Linear Model. Using a first-order Taylor approximation in terms of the temporal derivative of a canonical hemodynamic response function, statistical parametric maps of differential latencies were estimated via the ratio of derivative to canonical parameter estimates. This method was applied to two example datasets: comparison of words versus nonwords in a lexical decision task and initial versus repeated presentations of faces in a fame-judgment task. Tests across subjects revealed both magnitude and latency differences within several brain regions. This approach offers a computationally efficient means of detecting BOLD latency differences over the whole brain. Precise characterization of the hemodynamic latency and its interpretation in terms of underlying neural differences remain problematic, however.

Evidence for an Attentional Component of the Perceptual Misalignment between Moving and Flashing Stimuli

If a pair of dots, diametrically opposed to each other, is flashed in perfect alignment with another pair of dots rotating about the visual fixation point, most observers perceive the rotating dots as being ahead of the flashing dots (flash-lag effect). This psychophysical effect was first interpreted as the result of a perceptual extrapolation of the position of the moving dots. Also, it has been conceived as the result of differential visual latencies between flashing and moving stimuli, arising from purely sensory factors and/or expressing the contribution of attentional mechanisms as well. In a series of two experiments, we had observers judge the relative position between rotating and static dots at the moment a temporal marker was presented in the visual field. In experiment 1 we manipulated the nature of the temporal marker used to prompt the alignment judgment. This resulted in three main findings: (i) the flash-lag effect was observed to depend on the visual eccentricity of the flashing dots; (ii) the magnitude of the flash-lag effect was not dependent on the offset of the flashing dot; and (iii) the moving stimulus, when suddenly turned off, was perceived as lagging behind its disappearance location. Taken altogether, these results suggest that neither visible persistence nor motion extrapolation can account for the perceptual flash-lag phenomenon. The participation of attentional mechanisms was investigated in experiment 2, where the magnitude of the flash-lag effect was measured under both higher and lower predictability of the location of the flashing dot. Since the magnitude of the flash-lag effect significantly increased with decreasing predictability, we conclude that the observer's attentional set can modulate the differential latencies determining this perceptual effect. The flash-lag phenomenon can thus be conceived as arising from differential visual latencies which are determined not only by the physical attributes of the stimulus, such as its luminance or eccentricity, but also by attentional mechanisms influencing the delays involved in the perceptual processing.

The Position of Moving Objects

Eagleman and Sejnowski ([1][1]) showed that the flash-lag effect ([2][2], [3][3])—a visual illusion in which two objects physically at the same location appear to be offset because of differing motion trajectories—cannot be explained by latency correction ([4][4]) or by differential latencies