The role of ascorbate in antioxidant protection of biomembranes: Interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44796/1/10863_2004_Article_BF00762775.pd

Dynamic Tactile Information is Sufficient for Precise Curvature Discrimination

Our tactile perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration enhances the tactile perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 14 older adults to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. The curvature discrimination thresholds obtained for passive-dynamic touch were significantly lower than those that occurred during active-dynamic touch. This result demonstrates that active exploratory movements of the hand and fingers do not necessarily lead to the best curvature discrimination performance; rather, performance was best in the current study when dynamic tactile stimulation occurred in the absence of active movement. The results of the present study also clarify those obtained by Norman et al. (2013), who found that active-dynamic touch was superior to static touch -- the current findings extend this previous research and indicate that passive-dynamic touch can yield performance that is even higher than what is obtained for active-dynamic touch

Aging and curvature discrimination from static and dynamic touch.

Two experiments evaluated the ability of 30 older and younger adults to discriminate the curvature of simple object surfaces from static and dynamic touch. The ages of the older adults ranged from 66 to 85 years, while those of the younger adults ranged from 20 to 29 years. For each participant in both experiments, the minimum curvature magnitude needed to reliably discriminate between convex and concave surfaces was determined. In Experiment 1, participants used static touch to make their judgments of curvature, while dynamic touch was used in Experiment 2. When static touch was used to discriminate curvature, a large effect of age occurred (the thresholds were 0.67 & 1.11/m for the younger and older participants, respectively). However, when participants used dynamic touch, there was no significant difference between the ability of younger and older participants to discriminate curvature (the thresholds were 0.58 & 0.59/m for the younger and older participants, respectively). The results of the current study demonstrate that while older adults can accurately discriminate surface curvature from dynamic touch, they possess significant impairments for static touch

Perceiving Object Shape from Specular Highlight Deformation, Boundary Contour Deformation, and Active Haptic Manipulation.

It is well known that motion facilitates the visual perception of solid object shape, particularly when surface texture or other identifiable features (e.g., corners) are present. Conventional models of structure-from-motion require the presence of texture or identifiable object features in order to recover 3-D structure. Is the facilitation in 3-D shape perception similar in magnitude when surface texture is absent? On any given trial in the current experiments, participants were presented with a single randomly-selected solid object (bell pepper or randomly-shaped "glaven") for 12 seconds and were required to indicate which of 12 (for bell peppers) or 8 (for glavens) simultaneously visible objects possessed the same shape. The initial single object's shape was defined either by boundary contours alone (i.e., presented as a silhouette), specular highlights alone, specular highlights combined with boundary contours, or texture. In addition, there was a haptic condition: in this condition, the participants haptically explored with both hands (but could not see) the initial single object for 12 seconds; they then performed the same shape-matching task used in the visual conditions. For both the visual and haptic conditions, motion (rotation in depth or active object manipulation) was present in half of the trials and was not present for the remaining trials. The effect of motion was quantitatively similar for all of the visual and haptic conditions-e.g., the participants' performance in Experiment 1 was 93.5 percent higher in the motion or active haptic manipulation conditions (when compared to the static conditions). The current results demonstrate that deforming specular highlights or boundary contours facilitate 3-D shape perception as much as the motion of objects that possess texture. The current results also indicate that the improvement with motion that occurs for haptics is similar in magnitude to that which occurs for vision

Results of Experiment 2.

<p>The participants’ shape-matching accuracies (in terms of percent correct) are plotted as functions of both 1) the stimulus presentation type and 2) stimulus object complexity (the 8 stimulus objects were partitioned into two groups possessing low and high stimulus complexity). BC = boundary contours only, SH = specular highlights only, SH+BC = specular highlights with accompanying boundary contours, VT+BC = volumetric texture with accompanying boundary contours, H = haptic manipulation. The error bars indicate ± 1 SE. The dashed line indicates chance performance.</p

Results of Experiment 2.

<p>The participants’ shape-matching accuracies (in terms of percent correct) are plotted as functions of both 1) the stimulus presentation type and 2) the presence or absence of object motion/active haptic manipulation. BC = boundary contours only, SH = specular highlights only, SH+BC = specular highlights with accompanying boundary contours, VT+BC = volumetric texture with accompanying boundary contours, H = haptic manipulation. The error bars indicate ± 1 SE. The dashed line indicates chance performance.</p

A sequence of views of a shiny solid object (bell pepper 11) rotating in depth; the views progress from the upper-left (first view) to the bottom-right (last view).

<p>The object in each view has been rotated by 20 degrees from its orientation in the previous view. It is important to note that the shiny specular highlights deform quite radically over time in response to the object rotation in depth relative to the environmental light source. Note also that the object’s outer boundary contour also deforms in a complicated manner over time. Both types of motion (specular highlight and boundary contour deformation) differ qualitatively from the optical motions of surface texture elements (when they exist).</p

A photograph of the naturally-shaped solid objects (replicas of bell peppers, <i>Capsicum annuum</i>) used in Experiment 1.

<p>They are arranged in numerical order (1–12) from top-left to bottom right. These objects (and subsets of them) have been used in multiple previous investigations [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149058#pone.0149058.ref018" target="_blank">18</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149058#pone.0149058.ref026" target="_blank">26</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149058#pone.0149058.ref028" target="_blank">28</a>].</p

Results of Experiment 1.

<p>The participants’ shape-matching accuracies (in terms of percent correct) are plotted as functions of both 1) the stimulus presentation type and 2) the presence or absence of object motion/active haptic manipulation. BC = boundary contours only, SH = specular highlights only, SH+BC = specular highlights with accompanying boundary contours, VT+BC = volumetric texture with accompanying boundary contours, H = haptic manipulation. The error bars indicate ± 1 SE. The dashed line indicates chance performance.</p