Optimal visual-haptic integration with articulated tools

When we feel and see an object, the nervous system integrates visual and haptic information optimally, exploiting the redundancy in multiple signals to estimate properties more precisely than is possible from either signal alone. We examined whether optimal integration is similarly achieved when using articulated tools. Such tools (tongs, pliers, etc) are a defining characteristic of human hand function, but complicate the classical sensory ‘correspondence problem’ underlying multisensory integration. Optimal integration requires establishing the relationship between signals acquired by different sensors (hand and eye) and, therefore, in fundamentally unrelated units. The system must also determine when signals refer to the same property of the world—seeing and feeling the same thing—and only integrate those that do. This could be achieved by comparing the pattern of current visual and haptic input to known statistics of their normal relationship. Articulated tools disrupt this relationship, however, by altering the geometrical relationship between object properties and hand posture (the haptic signal). We examined whether different tool configurations are taken into account in visual–haptic integration. We indexed integration by measuring the precision of size estimates, and compared our results to optimal predictions from a maximum-likelihood integrator. Integration was near optimal, independent of tool configuration/hand posture, provided that visual and haptic signals referred to the same object in the world. Thus, sensory correspondence was determined correctly (trial-by-trial), taking tool configuration into account. This reveals highly flexible multisensory integration underlying tool use, consistent with the brain constructing internal models of tools’ properties. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00221-017-4896-5) contains supplementary material, which is available to authorized users

Analysis of a model for ethanol production through continuous fermentation: ethanol productivity

We investigate a model for the production of ethanol through continuous fermentation using Saccharomyces cerevisiae in a single reactor and cascades of up to five reactors. Using path-following methods we investigate how the ethanol productivity varies with the residence time in each reactor of the cascade. With a substrate feed concentration of 160 g/l we find the optimal productivity is 3.80 g/l/h, 5.08 g/l/h, and 5.18 g/l/h in a single reactor, a double reactor cascade and a triple reactor cascade respectively. For the case of a cascade containing reactors of equal size we investigate reactor configurations of up to five reactors and find that the maximum productivity is obtained in a cascade containing three reactors

Neural representations of haptic object size in the human brain revealed by multivoxel fMRI patterns

: The brain must interpret sensory input from diverse receptor systems to estimate object properties. Much has been learned about the brain mechanisms behind these processes in vision, but our understanding of haptic perception remains less clear. Here we examined haptic judgments of object size, which require integrating multiple cutaneous and proprioceptive afferent signals, as a model problem. To identify candidate human brain regions that support this process, participants (n = 16) in an event-related functional MRI experiment grasped objects to categorize them as one of four sizes. Object sizes were calibrated psychophysically to be equally distinct for each participant. We applied representational similarity logic to whole brain, multivoxel searchlight analyses to identify brain regions that exhibit size-relevant voxelwise activity patterns. Of particular interest was to identify regions for which more similar sizes produce more similar patterns of activity, which constitutes evidence of a metric size code. Regions of the intraparietal sulcus and the lateral prefrontal cortex met this criterion, both within hands and across hands. We suggest that these regions compute representations of haptic size that abstract over the specific peripheral afferent signals generated in a grasp. Results of a matched visual size task, performed by the same participants and analyzed in the same fashion, identified similar regions, indicating that these representations may be partly modality general. We consider these results with respect to perspectives on magnitude estimation in general and to computational views on perceptual signal integration.NEW & NOTEWORTHY Our understanding of the neural basis of haptics (perceiving the world through touch) remains incomplete. We used functional MRI to study human haptic judgments of object size, which require integrating multiple afferent signals. Multivoxel pattern analyses identified intraparietal and prefrontal regions that encode size haptically in a metric and hand-invariant fashion. Effector-independent haptic size estimates are useful on their own and in combination with other sensory estimates for a variety of perceptual and motor tasks

The relationship between oxidised LDL, endothelial progenitor cells and coronary endothelial function in patients with CHD

Objective The balance between coronary endothelial dysfunction and repair is influenced by many protective and deleterious factors circulating in the blood. We studied the relationship between oxidised low-density lipoprotein (oxLDL), circulating endothelial progenitor cells (EPCs) and coronary endothelial function in patients with stable coronary heart disease (CHD). Methods 33 patients with stable CHD were studied. Plasma oxLDL was measured using ELISA, coronary endothelial function was assessed using intracoronary acetylcholine infusion and EPCs were quantified using flow cytometry for CD34+/KDR+ cells. Results Plasma oxLDL correlated positively with the number of EPCs in the blood (r=0.46, p=0.02). There was a positive correlation between the number of circulating EPCs and coronary endothelial function (r=0.42, p=0.04). There was no significant correlation between oxLDL and coronary endothelial function. Conclusions Plasma levels of oxLDL are associated with increased circulating EPCs in the blood of patients with CHD, which may reflect a host-repair response to endothelial injury. Patients with stable CHD had a high prevalence of coronary endothelial dysfunction, which was associated with lower numbers of circulating EPCs, suggesting a mechanistic link between endothelial dysfunction and the pathogenesis of atherosclerosis

Visual-haptic integration with pliers and tongs: signal “weights” take account of changes in haptic sensitivity caused by different tools.

When we hold an object while looking at it, estimates from visual and haptic cues to size are combined in a statistically optimal fashion, whereby the “weight” given to each signal reflects their relative reliabilities. This allows object properties to be estimated more precisely than would otherwise be possible. Tools such as pliers and tongs systematically perturb the mapping between object size and the hand opening. This could complicate visual-haptic integration because it may alter the reliability of the haptic signal, thereby disrupting the determination of appropriate signal weights. To investigate this we first measured the reliability of haptic size estimates made with virtual pliers-like tools (created using a stereoscopic display and force-feedback robots) with different “gains” between hand opening and object size. Haptic reliability in tool use was straightforwardly determined by a combination of sensitivity to changes in hand opening and the effects of tool geometry. The precise pattern of sensitivity to hand opening, which violated Weber's law, meant that haptic reliability changed with tool gain. We then examined whether the visuo-motor system accounts for these reliability changes. We measured the weight given to visual and haptic stimuli when both were available, again with different tool gains, by measuring the perceived size of stimuli in which visual and haptic sizes were varied independently. The weight given to each sensory cue changed with tool gain in a manner that closely resembled the predictions of optimal sensory integration. The results are consistent with the idea that different tool geometries are modeled by the brain, allowing it to calculate not only the distal properties of objects felt with tools, but also the certainty with which those properties are known. These findings highlight the flexibility of human sensory integration and tool-use, and potentially provide an approach for optimizing the design of visual-haptic devices

A stereo display prototype with multiple focal distances

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