Mechanical Effects of Canes on Postural Control: Beyond Perceptual Information

BackgroundNumerous studies showed that postural balance improves through light touch on a stable surface highlighting the importance of haptic information, seemingly downplaying the mechanical contributions of the support. The present study examined the mechanical effects of canes for assisting balance in healthy individuals challenged by standing on a beam. MethodsSixteen participants supported themselves with two canes, one in each hand, and applied minimal, preferred, or maximum force onto the canes. They positioned the canes in the frontal plane or in a tripod configuration. ResultsResults showed that canes significantly reduced the variability of the center of pressure and center of mass to the same level as when standing on the ground. In the preferred condition, participants exploited the altered mechanics by resting their arms on the canes and, in the tripod configuration, allowing for larger CoP motions in the task-irrelevant dimension. Increasing the exerted force beyond the preferred level yielded no further benefits, in fact had a destabilizing effect on the canes: the displacement of the hand on the cane handle increased with the force. ConclusionsDespite the challenge of a statically unstable system, these results show that, in addition to augmenting perceptual information, using canes can provide mechanical benefits and challenges. First, the controller minimizes effort channeling noise in the task-irrelevant dimensions and, second, resting the arms on the canes but avoiding large forces that would have destabilizing effects. However, if maximal force is applied to the canes, the instability of the support needs to be counteracted, possibly by arm and shoulder stiffness.

Attention in Discrimination Learning: a Stimulus Control Approach to the Intradimensional-Extradimensional Shift Paradigm

<p>In the present thesis, the intradimensional-extradimensional shift effect was treated as a problem of two-dimensional stimulus control. Factors determining stimulus control in the ID-ED shift were explored over six experiments. In Experiment 1 adult students were trained to discriminate between successively presented stimuli that differed in both line length and orientation. For half the subjects the length dimension was relevant (ie: different stimuli on that dimension were correlated with different outcomes) and for half the subjects orientation was relevant (phase 1). All subjects were then shifted to a second discrimination between new line lengths and orientations (Phase 2). For half, this constituted an intradimensional (ID) shift in that the previously relevant dimension remained relevant; for the remaining subjects the previously irrelevant dimension was made relevant in an extradimensional (ED) shift. The ID shift required significantly fewer trials to establish strong stimulus control by the relevant dimension in Phase 2 than did the ED shift. Experiments 1 and 2 further established that such differences were not attributable to a dominance relationship between dimensions or to specific cue values. Experiment 3 examined the development of stimulus control by the two dimensions over trials in Phase 2. In the ED shift, two-dimensional generalisation gradients showed a systematic weakening and strengthening of control by the Phase 1 relevant and Phase 2 relevant dimensions respectively. In the ID shift there was no change in stimulus control by either dimension. Experiment 4 established that transfer to the orientation dimension following differential training on length (ED shift) was superior to orientation following non-differential training on length (PD shift). Learning that differences on an extradimensional dimension were relevant in Phase I therefore had a facilitatory effect on control by orientation. Experiments 5 and 6 investigated the effects of manipulating the number of cues on the irrelevant Phase 1 dimension (orientation) and/or the irrelevant phase 2 dimension (length), in an ED shift where orientation was relevant in Phase 2. Both orientation and length (Experiment 5) or orientation alone (Experiment 6) were varied in the generalisation test. The ED shift in Phase 2 was retarded by the irrelevant dimension in Phase 1. It was concluded that in general the phase I relevant dimension must lose control in Phase 2, and the phase 1 irrelevant dimension must gain control in Phase 2 (Experiment 3). However, the inverse relation between loss of control by one dimension and gaining of control by the other does not occur in a way consistent with the Inverse Hypothesis of some selective attention theories. In addition, the previously relevant dimension in an ED shift facilitates control by the new relevant dimension in phase 2 re1ative to non-differential training, consistent with attentional enhancement. The major factor found to be slowing down the development of control by the new relevant dimension in an ED shift is the presence of the irrelevant dimension in Phase 1, (Experiment 5). This is probably a 'learned irrelevance' effect.</p>

Position and Identity in Visual Information Processing

<p>Information that is presented visually can be described in terms of its identity and in terms of its position, and a distinction can be drawn between what an item is and where that item is. For example, a letter displayed on a screen has both an identity (its name) and a spatial position; the spatial position can be specified either absolutely (the upper right quadrant) or relatively (beside the "x" and above the "y"). There is an obvious and intimate relationship between the identity component and the position component, and it is this relationship, between the the processing of position information and the processing of identity information, that forms the subject of the present thesis. First, the relevant I literature is reviewed. The relationship between position and identity is examined in the context of two major research areas: iconic memory and short term visual memory. Second, the concept of dimensional separability is considered with reference to the appropriate literature. The purpose is to indicate a theoretical framework within which the issue of concern may be profitably addressed. The key idea to be developed is that position and identity are asymmetrically separable dimensions. A small group of studies that offer tentative support to this conceptualization will be discussed. Third, the results of eight related experiments are reported. These experiments involve the recognition of position and/or identity information in a discrete trials procedure. The eight experiments fall into three separate groups. Experiments 1 to 3 examine the recognition of either position or identity information, with the two types of information presented in relative isolation. Several stimulus factors are manipulated in order to demonstrate differential effects upon the two dimensions. Experiments 4 to 6 examine the effect of the irrelevant dimension upon recognition of the relevant dimension. Experiment 4 uses a logically balanced set of stimuli, so that the irrelevant dimension is either consistent or inconsistent, whereas in Experiments 5 and 6 each dimension is examined in the context of consistent, inconsistent, or neutral information on the irrelevant dimension. Experiments 7 and 8 explore the integration of position and identity information by varying the task requirements. Shared attention conditions are contrasted with selective attention conditions to show the impact of attentional strategy. The thesis concludes with a general discussion of the results, and their accordance with the hypothesis of asymmetric separability.</p>

Attention in Discrimination Learning: a Stimulus Control Approach to the Intradimensional-Extradimensional Shift Paradigm

<p>In the present thesis, the intradimensional-extradimensional shift effect was treated as a problem of two-dimensional stimulus control. Factors determining stimulus control in the ID-ED shift were explored over six experiments. In Experiment 1 adult students were trained to discriminate between successively presented stimuli that differed in both line length and orientation. For half the subjects the length dimension was relevant (ie: different stimuli on that dimension were correlated with different outcomes) and for half the subjects orientation was relevant (phase 1). All subjects were then shifted to a second discrimination between new line lengths and orientations (Phase 2). For half, this constituted an intradimensional (ID) shift in that the previously relevant dimension remained relevant; for the remaining subjects the previously irrelevant dimension was made relevant in an extradimensional (ED) shift. The ID shift required significantly fewer trials to establish strong stimulus control by the relevant dimension in Phase 2 than did the ED shift. Experiments 1 and 2 further established that such differences were not attributable to a dominance relationship between dimensions or to specific cue values. Experiment 3 examined the development of stimulus control by the two dimensions over trials in Phase 2. In the ED shift, two-dimensional generalisation gradients showed a systematic weakening and strengthening of control by the Phase 1 relevant and Phase 2 relevant dimensions respectively. In the ID shift there was no change in stimulus control by either dimension. Experiment 4 established that transfer to the orientation dimension following differential training on length (ED shift) was superior to orientation following non-differential training on length (PD shift). Learning that differences on an extradimensional dimension were relevant in Phase I therefore had a facilitatory effect on control by orientation. Experiments 5 and 6 investigated the effects of manipulating the number of cues on the irrelevant Phase 1 dimension (orientation) and/or the irrelevant phase 2 dimension (length), in an ED shift where orientation was relevant in Phase 2. Both orientation and length (Experiment 5) or orientation alone (Experiment 6) were varied in the generalisation test. The ED shift in Phase 2 was retarded by the irrelevant dimension in Phase 1. It was concluded that in general the phase I relevant dimension must lose control in Phase 2, and the phase 1 irrelevant dimension must gain control in Phase 2 (Experiment 3). However, the inverse relation between loss of control by one dimension and gaining of control by the other does not occur in a way consistent with the Inverse Hypothesis of some selective attention theories. In addition, the previously relevant dimension in an ED shift facilitates control by the new relevant dimension in phase 2 re1ative to non-differential training, consistent with attentional enhancement. The major factor found to be slowing down the development of control by the new relevant dimension in an ED shift is the presence of the irrelevant dimension in Phase 1, (Experiment 5). This is probably a 'learned irrelevance' effect.</p>

Position and Identity in Visual Information Processing

<p>Information that is presented visually can be described in terms of its identity and in terms of its position, and a distinction can be drawn between what an item is and where that item is. For example, a letter displayed on a screen has both an identity (its name) and a spatial position; the spatial position can be specified either absolutely (the upper right quadrant) or relatively (beside the "x" and above the "y"). There is an obvious and intimate relationship between the identity component and the position component, and it is this relationship, between the the processing of position information and the processing of identity information, that forms the subject of the present thesis. First, the relevant I literature is reviewed. The relationship between position and identity is examined in the context of two major research areas: iconic memory and short term visual memory. Second, the concept of dimensional separability is considered with reference to the appropriate literature. The purpose is to indicate a theoretical framework within which the issue of concern may be profitably addressed. The key idea to be developed is that position and identity are asymmetrically separable dimensions. A small group of studies that offer tentative support to this conceptualization will be discussed. Third, the results of eight related experiments are reported. These experiments involve the recognition of position and/or identity information in a discrete trials procedure. The eight experiments fall into three separate groups. Experiments 1 to 3 examine the recognition of either position or identity information, with the two types of information presented in relative isolation. Several stimulus factors are manipulated in order to demonstrate differential effects upon the two dimensions. Experiments 4 to 6 examine the effect of the irrelevant dimension upon recognition of the relevant dimension. Experiment 4 uses a logically balanced set of stimuli, so that the irrelevant dimension is either consistent or inconsistent, whereas in Experiments 5 and 6 each dimension is examined in the context of consistent, inconsistent, or neutral information on the irrelevant dimension. Experiments 7 and 8 explore the integration of position and identity information by varying the task requirements. Shared attention conditions are contrasted with selective attention conditions to show the impact of attentional strategy. The thesis concludes with a general discussion of the results, and their accordance with the hypothesis of asymmetric separability.</p>

Number symbols are processed more automatically than nonsymbolic numerical magnitudes: Findings from a Symbolic-Nonsymbolic Stroop task

Are number symbols (e.g., 3) and numerically equivalent quantities (e.g., •••) processed similarly or distinctly? If symbols and quantities are processed similarly then processing one format should activate the processing of the other. To experimentally probe this prediction, we assessed the processing of symbols and quantities using a Stroop-like paradigm. Participants (NStudy1 = 80, NStudy2 = 63) compared adjacent arrays of symbols (e.g., 4444 vs 333) and were instructed to indicate the side containing either the greater quantity of symbols (nonsymbolic task) or the numerically larger symbol (symbolic task). The tasks included congruent trials, where the greater symbol and quantity appeared on the same side (e.g. 333 vs. 4444), incongruent trials, where the greater symbol and quantity appeared on opposite sides (e.g. 3333 vs. 444), and neutral trials, where the irrelevant dimension was the same across both sides (e.g. 3333 vs. 333 for nonsymbolic; 333 vs. 444 for symbolic). The numerical distance between stimuli was systematically varied, and quantities in the subitizing and counting range were analyzed together and independently. Participants were more efficient comparing symbols and ignoring quantities, than comparing quantities and ignoring symbols. Similarly, while both symbols and quantities influenced each other as the irrelevant dimension, symbols influenced the processing of quantities more than quantities influenced the processing of symbols, especially for quantities in the counting rage. Additionally, symbols were less influenced by numerical distance than quantities, when acting as the relevant and irrelevant dimension. These findings suggest that symbols are processed differently and more automatically than quantities.

Exact summation of leading logs around $$ T\overline{T} $$ deformation of O(N + 1)-symmetric 2D QFTs

We consider a general (beyond $$ T\overline{T} $$ T T ¯ ) deformation of the 2D O(N + 1) σ-model by the irrelevant dimension-four operators. The theory deformed in this most general way is not integrable, and the S-matrix loses its factorization properties. We perform the all-order summation of the leading infrared logs for the 2 → 2 scattering amplitude and provide the exact result for the 2 → 2 S-matrix in the leading logarithmic approximation. These results can provide us with new insights into the properties of the theories deformed by irrelevant operators more general than the $$ T\overline{T} $$ T T ¯ deformation.

When unsupervised training benefits category learning

Humans continuously categorise inputs, but only rarely receive explicit feedback as to whether or not they are correct. This implies that they may be integrating unsupervised information together with their sparse supervised data -- a form of semi-supervised learning. However, experiments testing semi-supervised learning are rare, and are bedevilled with conflicting results about whether the unsupervised information affords any benefit. Here, we suggest that one important factor that has been paid insufficient attention is the alignment between subjects' internal representations of the stimulus material and the experimenter-defined representations that determine success in the tasks. Subjects' representations are shaped by prior biases and experience, and unsupervised learning can only be successful if the alignment suffices. Otherwise, unsupervised learning might harmfully strengthen incorrect assumptions. To test this hypothesis, we conducted an experiment in which subjects initially categorise items along a salient, but task-irrelevant, dimension, and only recover the correct categories when sufficient feedback draws their attention to the subtle, task-relevant, stimulus dimensions. By withdrawing feedback at different stages along this learning curve, we tested whether unsupervised learning improves or worsens performance when internal stimulus representations and task are sufficiently or insufficiently aligned, respectively. Our results demonstrate that unsupervised learning can indeed have opposing effects on subjects' learning. We also discuss factors limiting the degree to which such effects can be predicted from momentary performance. Our work implies that predicting and understanding human category learning in particular tasks requires assessment and consideration of the representational spaces that subjects entertain for the materials involved in those tasks. These considerations not only apply to studies in the lab, but could also help improve the design of tutoring systems and instruction.

Event-based encoding of biological motion and location in visual working memory

We make use of discrete yet meaningful events to orient ourselves to the dynamic environment. Among these events, biological motion, referring to the movements of animate entities, is one of the most biologically salient. We usually encounter biological motions of multiple human beings taking place simultaneously at distinct locations. How we encode biological motions into visual working memory (VWM) to form a coherent experience of the external world and guide our social behaviour remains unclear. This study for the first time addressed the VWM encoding mechanism of biological motions and their corresponding locations. We tested an event-based encoding hypothesis for biological motion and location: When one element of an event is required to be memorised, the irrelevant element of an event will also be extracted into VWM. We presented participants with three biological motions at different locations and required them to memorise only the biological motions or their locations while ignoring the other dimension. We examined the event-based encoding by probing a distracting effect: If the event-based encoding took place, the change of irrelevant dimension in the probe would lead to a significant distraction and impair the performance of detecting target dimension. We found significant distracting effects, which lasted for 3 s but vanished at 6 s, regardless of the target dimension (biological motions vs. locations, Experiment 1) and the exposure time of memory array (1 s vs. 3 s, Experiment 2). These results together support an event-based encoding mechanism during VWM encoding of biological motions and their corresponding locations.

Further tests of sequence-sensitive models in a modified Garner task using separable dimensions

In the study of perceptual categorization, a key distinction is made between integral and separable dimensions. Integral dimensions are often highly unanalyzable, while separable dimensions are highly analyzable and easy to attend in isolation. Little, Wang, and Nosofsky (2016) showed that when trial-by-trial responses are analyzed, a consistent pattern of sequential effects was found in a modified Garner paradigm using integral-dimension stimuli. The present experiments investigate whether these pronounced sequential effects are also found with separable-dimension stimuli. Two experiments using different separable dimensions were conducted. The results indicate that similar patterns of sequential effects were present for separable dimension stimuli, but, unlike for integral dimensions, the effect of a change in the irrelevant dimension in the filtering task was not found. Further, for separable dimensions, the overall pattern of sequential effects did not vary between the Garner tasks (i.e., control, correlated, and filtering). To explain these results, we fit a sequence-sensitive exemplar model and compared the fits of this model to a novel sequence-sensitive feature model, in which only the relevant feature influences the categorization decision. We find that this feature-based model provides a more compelling account of our separable dimension data, while the full exemplar model provides a better account of the integral dimension data. The findings of the present study provide a morecomplete understanding of perceptual categorization and add to the growing body of literature on the prevalence and critical implications of strong sequential effects in cognitive tasks.