Effects of visual focus and gait speed on walking balance in the frontal plane

We investigated how head position and gait speed influenced frontal plane balance responses to external perturbations during gait. Thirteen healthy participants walked on a treadmill at three different gait speeds. Visual conditions included either focus downward on lower extremities and walking surface only or focus forward on a stationary scene with horizontal and vertical lines. The treadmill was positioned on a platform that was stationary (non-perturbed) or moving in a pattern that appeared random to the subjects (perturbed). In non-perturbed walking, medial–lateral upper body motion was very similar between visual conditions. However, in perturbed walking, there was significantly less body motion when focus was on the stationary visual scene, suggesting visual feedback of stationary vertical and horizontal cues are particularly important when balance is challenged. Sensitivity of body motion to perturbations was significantly decreased by increasing gait speed, suggesting that faster walking was less sensitive to frontal plane perturbations. Finally, our use of external perturbations supported the idea that certain differences in balance control mechanisms can only be detected in more challenging situations, which is an important consideration for approaches to investigating sensory contribution to balance during gait.     

The impact of speed and time on gait dynamics

To determine the effects of speed on gait previous studies have examined young adults walking at different speeds; however, the small number of strides may have influenced the results. The aim of this study was to investigate the immediate and long-term impact of continuous slow walking on the mean, variability and structure of stride-to-stride measures. Fourteen young adults walked at a constant pace on a treadmill at three speeds (preferred walking speed (PWS), 90% and 80% PWS) for 30 min each. Spatiotemporal gait parameters were computed over six successive 5-min intervals. Walking slower significantly decreased stride length, while stride period and width increased. Additionally, stride period and width variability increased. Signal regularity of stride width increased and decreased in stride period. Persistence of stride period and width increased significantly at slower speeds. While several measures changed during 30 min of walking, only stride period variability and signal regularity revealed a significant speed and time interaction. Healthy young adults walking at slower than preferred speeds demonstrated greater persistence and signal regularity of stride period while spatiotemporal changes such as increased stride width and period variability arose. These results suggest that different control processes are involved in adapting to the slower speeds.     

Manipulation of visual information does not change the accuracy of distance estimation during a blindfolded walking task

While humans rely on vision during navigation, they are also competent at navigating non-visually. However, non-visual navigation over large distances is not very accurate and can accumulate error. Currently, it is unclear whether this accumulation of error is due to the visual estimate of the distance or to the locomotor production of the distance. In a series of experiments, using a blindfolded walking test, we examine whether enhancing the visual estimate of the distance to a previously seen target, through environmental enrichment, visual imagery, or repeated exposure would improve the accuracy of blindfold navigation across different distances. We also attempt to decrease the visual estimate in order to see if the opposite effect would occur. Our results would indicate that manipulation of the static visual distance estimate did not change the navigation accuracy to any great extent. The only condition that improved accuracy was repeated exposure to the environment through practice. These results suggest that error observed during blindfold navigation may be due to the locomotor production of the distance, rather than the visual process.     

The influence of a long term exercise program on lower limb movement variability and walking performance in patients with peripheral arterial disease

The purpose of this study was to examine the effects of a 12 month exercise program on lower limb movement variability in patients with peripheral arterial disease (PAD). Participants (n = 21) with an appropriate history of PAD and intermittent claudication (IC) volunteered for this study and were randomly allocated to either a control group (CPAD–IC) (n = 11), which received normal medical therapy and a treatment group (TPAD–IC) (n = 10), which received normal medical therapy treatment and a 12 month supervised exercise program. All participants underwent 2D joint angular kinematic analysis during normal walking to assess lower limb movement variability and walking speed. Between-group differences were analyzed via mixed measures ANOVA. The 12 month supervised exercise program made no significant impact on the lower limb movement variability or walking speed of the TPAD–IC group as determined by either intralimb joint coordination or single joint analysis techniques. Long term supervised exercise programs do not appear to influence the lower limb movement variability of PAD–IC patients.     

The effects of sub-threshold vibratory noise on visuomotor entrainment during human walking and standing in a virtual reality environment

Humans will naturally synchronize their posture to the motion of a visual surround, but it is unclear if this visuomotor entrainment can be attenuated with an increased sensitivity to somatosensory information. Sub-threshold vibratory noise applied to the Achilles tendons has proven to enhance ankle proprioception through the phenomenon of stochastic resonance. Our purpose was to compare visuomotor entrainment during walking and standing, and to understand how this entrainment might be attenuated by applying sub-threshold vibratory noise over the Achilles tendons. We induced visuomotor entrainment during standing and treadmill walking for ten subjects (24.5 ± 2.9 years) using a speed-matched virtual hallway with continuous mediolateral perturbations at three different frequencies. Vibrotactile motors over the Achilles tendons provided noise (0–400 Hz) with an amplitude set to 90% of each participant’s sensory threshold. Mediolateral sacrum, C7, and head motion was greatly amplified (4–8× on average) at the perturbation frequencies during walking, but was much less pronounced during standing. During walking, individuals with greater mediolateral head motion at the fastest perturbation frequency saw the greatest attenuation of that motion with applied noise. Similarly, during standing, individuals who exhibited greater postural sway (as measured by the center of pressure) also saw the greatest reductions in sway with sub-threshold noise applied in three of our summary metrics. Our results suggest that, at least for healthy young adults, sub-threshold vibratory noise over the Achilles tendons can slightly improve postural control during disruptive mediolateral visual perturbations, but the applied noise does not substantially attenuate visuomotor entrainment during walking or standing.     

The ventriloquist effect does not depend on the direction of deliberate visual attention

It is well known that discrepancies in the location of synchronized auditory and visual events can lead to mislocalizations of the auditory source, so-called ventriloquism. In two experiments, we tested whether such cross-modal influences on auditory localization depend on deliberate visual attention to the biasing visual event. In Experiment 1, subjects pointed to the apparent source of sounds in the presence or absence of a synchronous peripheral flash. They also monitored for target visual events, either at the location of the peripheral flash or in a central location. Auditory localization was attracted toward the synchronous peripheral flash, but this was unaffected by where deliberate visual attention was directed in the monitoring task. In Experiment 2, bilateral flashes were presented in synchrony with each sound, to provide competing visual attractors. When these visual events were equally salient on the two sides, auditory localization was unaffected by which side subjects monitored for visual targets. When one flash was larger than the other, auditory localization was slightly but reliably attracted toward it, but again regardless of where visual monitoring was required. We conclude that ventriloquism largely reflects automatic sensory interactions, with little or no role for deliberate spatial attention.     

The ventriloquist effect does not depend on the direction of automatic visual attention

Previously, we showed that the visual bias of auditory sound location, or ventriloquism, does not depend on the direction of deliberate, orendogenous, attention (Bertelson, Vroomen, de Gelder, & Driver, 2000). In the present study, a similar question concerning automatic, orexogenous, attention was examined. The experimental manipulation was based on the fact that exogenous visual attention can be attracted toward asingleton—that is, an item different on some dimension from all other items presented simultaneously. A display was used that consisted of a row of four bright squares with one square, in either the left- or the rightmost position,smaller than the others, serving as the singleton. In Experiment 1, subjects made dichotomous left-right judgments concerning sound bursts, whose successivelocations were controlled by a psychophysical staircase procedure and which were presented in synchrony with a display with the singleton either left or right. Results showed that the apparent location of the sound was attractednot toward the singleton, but instead toward the big squares at the opposite end of the display. Experiment 2 was run to check that the singleton effectively attracted exogenous attention. The task was to discriminate target letters presented either on the singleton or on the opposite big square. Performance deteriorated when the target was on the big square opposite the singleton, in comparison with control trials with no singleton, thus showing that the singleton attracted attention away from the target location. In Experiment 3, localization and discrimination trials were mixed randomly so as to control for potential differences in subjects’ strategies in the two preceding experiments. Results were as before, showing that the singleton attracted attention, whereas sound localization was shifted away from the singleton. Ventriloquism can thus be dissociated from exogenous visual attention and appears to reflect sensory interactions with little role for the direction of visual spatial attention.     

The ventriloquist effect does not depend on the direction of automatic visual attention.

Previously, we showed that the visual bias of auditory sound location, or ventriloquism, does not depend on the direction of deliberate, or endogenous, attention (Bertelson, Vroomen, de Gelder, & Driver, 2000). In the present study, a similar question concerning automatic, or exogenous, attention was examined. The experimental manipulation was based on the fact that exogenous visual attention can be attracted toward a singleton--that is, an item different on some dimension from all other items presented simultaneously. A display was used that consisted of a row of four bright squares with one square, in either the left- or the rightmost position, smaller than the others, serving as the singleton. In Experiment 1, subjects made dichotomous left-right judgments concerning sound bursts, whose successive locations were controlled by a psychophysical staircase procedure and which were presented in synchrony with a display with the singleton either left or right. Results showed that the apparent location of the sound was attracted not toward the singleton, but instead toward the big squares at the opposite end of the display. Experiment 2 was run to check that the singleton effectively attracted exogenous attention. The task was to discriminate target letters presented either on the singleton or on the opposite big square. Performance deteriorated when the target was on the big square opposite the singleton, in comparison with control trials with no singleton, thus showing that the singleton attracted attention away from the target location. In Experiment 3, localization and discrimination trials were mixed randomly so as to control for potential differences in subjects' strategies in the two preceding experiments. Results were as before, showing that the singleton attracted attention, whereas sound localization was shifted away from the singleton. Ventriloquism can thus be dissociated from exogenous visual attention and appears to reflect sensory interactions with little role for the direction of visual spatial attention.     

The recognition of phonologically assimilated words does not depend on specific language experience

In a series of 5 experiments, we investigated whether the processing of phonologically assimilated utterances is influenced by language learning. Previous experiments had shown that phonological assimilations, such as /lean#bacon/ → [leam bacon], are compensated for in perception. In this article, we investigated whether compensation for assimilation can occur without experience with an assimilation rule using automatic event-related potentials. Our first experiment indicated that Dutch listeners compensate for a Hungarian assimilation rule. Two subsequent experiments, however, failed to show compensation for assimilation by both Dutch and Hungarian listeners. Two additional experiments showed that this was due to the acoustic properties of the assimilated utterance, confirming earlier reports that phonetic detail is important in compensation for assimilation. Our data indicate that compensation for assimilation can occur without experience with an assimilation rule, in line with phonetic-phonological theories that assume that speech production is influenced by speech-perception abilities.     

The size of the cross-lingual masked phonological priming effect does not depend on second language proficiency

Using a masked phonological priming paradigm, Brysbaert, Van Dyck, and Van de Poel (1999) showed that Dutch-French bilinguals perform better at identifying tachistoscopically presented L2 words (e.g., oui [yes]) when those words are primed by L1 words or nonwords that are homophonic to the L2 target word according to the L1 grapheme-phoneme conversion rules (e.g., wie [who]). They noted that this priming effect was smaller for balanced bilinguals than for less proficient bilinguals, although the interaction failed to reach significance. Findings of Gollan, Forster, and Frost (1997) suggest that this could be attributed to a greater reliance on phonology in L2 reading, caused by a smaller proficiency in this language. However, in this study we show that the Dutch-French cross-lingual phonological priming effect is equally large for perfectly balanced and less proficient bilinguals. Our findings are in line with more recent work of Van Wijnendaele and Brysbaert (2002).     

The control of appetitive instrumental responding does not depend on classical conditioning to the discriminative stimulus

In Experiment I, rats were exposed to a classical relationship between a clicker-light compound and response-independent food. Conditioning to the light was blocked if the clicker had previously served as a classical signal for food, but not if it had been established as a discriminative stimulus for food-reinforced lever pressing. In Experiment II, a tone-light compound served as a discriminative stimulus for lever pressing. Control by the light was blocked if the tone was independently trained as a discriminative stimulus, but not if it was trained as a classical signal for response-independent food. These results suggest that discriminative stimuli do not come to control appetitive instrumental responding by virtue of their implicit classical relationship to the instrumental reinforcer.     

The effects of metronomic pendular adjustment versus tap-tempo input on the stability and accuracy of tempo perception

This study explores tempo stability and accuracy while comparing two subject-response modes: the traditional metronomic pendular adjustment task versus tap-tempo input. Experiment 1 questioned if a single correct tempo measurement consistently emerges from repeated listenings, and if subject-response mode affects tempo stability and accuracy. Experiment 2 assessed incremental improvement between two repeated sessions, and questioned the incidence of self-pacing or congruent effects of potential delays on tempo responses. While single-session studies have shown that listeners find some tempos more enjoyable, can notice discrete differences in pace, and can remember rhythmic speed over prolonged periods of time, the current study employs a multiple-session format focusing on two diametrically opposed subject-response modes. The findings show that tempo responses by listeners without formal music training were consistent across listening sessions, and that responses from tap-tempo input were significantly more stable and accurate than responses from metronomic pendular adjustment tasks.     

Knowledge does not necessarily make the heart grow fonder: The moderating role of knowledge on accessibility experiences

Accessibility experiences have been a subject of interest since Tversky and Kahneman (1973) published their account of the availability heuristic—specifically, individuals often utilize the phenomenological experience of ease or difficulty of recall in constructing a judgment (Schwarz, 1998). The reported studies contribute further to work in this area by examining the moderating role of knowledge on accessibility experiences and their use in evaluative judgments. We argue that knowledgeable individuals are more likely to experience interference effects in early stages of recall. This would result in a reversal of the usual phenomenon such that while low knowledge individuals would find recalling larger sets effortful, which would lead them to form more negative evaluations when recalling larger amounts of information, high knowledge individuals would find recalling smaller sets effortful and would form more negative evaluations when recalling smaller amounts of information. We discuss potential explanations and draw attention to the distinction between generating a response and the appropriateness of the response in accessibility experiences.     

Abiding by the law when it does not exist: The case of the helmet bicycle law

To improve the safety of bicycle users, some countries have enacted, or considered enacting, mandatory helmet legislation. Of course, the enactment of such legislation in a country assumes that its citizens will be well-informed of it, and consequently, will use the helmet more frequently than before. However, in the survey described in this paper we found that many people are not aware of the legislation in force in their own country, or, even if they know, they may not necessarily behave as dictated by the law. Thus, the effects of mandatory helmet legislation may be somewhat different than desired or expected. Therefore, the goal of this paper is to ascertain the role of cyclists’ knowledge of the law in their country as a mediator between the law and the actual use of the helmet. Respondents from seventeen countries participated in an international survey about cyclists' habits, and answered questions about helmet legislation, and frequency of helmet use. The results indicate that the main effect of mandatory helmet legislation on the frequency of use of the helmet is mediated by the perception that such a law exists in their country—even when in fact sometimes it does not exist.     

The effect of stopping before turning on the direct observational measure of whole body turning bias

Turning bias, the preferential tendency to turn toward a given direction has been reported in both rodents and human participants. The observational gait method of determining turning bias in humans requires a stop prior to turning. This study removed the stop and hypothesised that turning bias would remain the same between stop and non-stop conditions if bias was solely under the control of neurochemical asymmetries. The results showed that statistically turning bias remained the same (to the left) regardless of method used but there was no agreement between the methods thus rejecting the hypothesis. It is likely that when not stopping biomechanical factors related to gait when turning influence the direction of turn rather than solely neurochemical asymmetries.     

Sub-optimal choice in pigeons does not depend on avoidance of the stimulus associated with the absence of reinforcement

When pigeons are given a choice between two alternatives, one leading to a stimulus 20% of the time that always signals reinforcement (S+) or another stimulus 80% of the time that signals no reinforcement (S−), and the other alternative leading to one of two stimuli each signaling reinforcement 50% of the time, they show a strong preference for the first alternative. This preference occurs in spite of the fact that, overall, the second alternative provides two and a half times more reinforcement than the first. In the present experiment we tested the hypothesis that the S− is a less effective conditioned inhibitor because as soon as it is recognized, the pigeon may orient away from it, whereas it does not orient away from the other signals. To test this hypothesis, for Group HLS−, we made the S− more salient and less avoidable by using a ceiling mounted houselight. To control for a possible aversion to the houselight we included Group HLS+, a group for which the houselight served as the S+. And the preferences of both groups were compared to those of a standard no houselight group. The pigeons in all three groups showed a strong preference for the lower probability of reinforcement alternative. Thus, reduced peripheral orienting during presentation of the S− stimulus was not likely responsible for pigeons’ sub-optimal choice.     

The effects of study order and backward associative strength on illusory recollection: A source-strength effect does not always occur

We investigated illusory recollection by dividing lists of associated words into three subsets (high, medium and low) based on their backward associative strength (BAS) to an unstudied theme. Participants studied these subsets at different visual locations on a computer screen and afterwards were given a source memory test. In Experiment 1, we varied the order in which high- and medium-BAS subsets were studied. In Experiment 2, we again manipulated study order as well as the associative strength of the medium-BAS subsets (strong or weak). Across both experiments, illusory recollection was constrained by both study order and BAS. Source attributions to the high-BAS location were more likely (a source-strength effect) when high-BAS items were studied first or studied following items of relatively low associative strength. However, attributions to the strong medium-BAS studied location were more likely when these items were studied before high-BAS items. These findings are interpreted as resulting from misbinding of source details at encoding which can be explained by the activation-monitoring theory of illusory recollection.     

Using the Implicit Association Test does not rule out an impact of conscious propositional knowledge on evaluative conditioning

Implicit measures such as the Implicit Association Test (IAT) have recently become popular as tools in research on evaluative conditioning. The reason is that these measures are thought to be impervious to changes in valence that are due to conscious propositional knowledge about the relation between the conditioned stimulus (CS) and the unconditioned stimulus (US). I present data that raise doubts about the validity of this assumption. In two experiments, attitudes towards CSs as measured by the IAT were in line with instructed CS-US contingencies even though the CSs and USs were never actually paired. The results therefore suggest that IAT effects can be biassed by conscious propositional knowledge.