Perceptual constancy of texture roughness in the tactile system.

Our tactual perception of roughness is independent of the manner in which we touch the surface. A brick surface feels rough no matter how slowly or how rapidly we move our fingers, despite the fluctuating sensory inputs that are transmitted to the finger. Current theories of roughness perception rely solely on inputs from the cutaneous afferents, which are highly affected by scan velocity and force.

Neural mechanisms of tactile motion integration in somatosensory cortex.

How are local motion signals integrated to form a global motion percept? We investigate the neural mechanisms of tactile motion integration by presenting tactile gratings and plaids to the fingertips of monkeys, using the tactile analogue of a visual monitor and recording the responses evoked in somatosensory cortical neurons. The perceived directions of the gratings and plaids are measured in parallel psychophysical experiments. We identify a population of somatosensory neurons that exhibit integration properties comparable to those induced by analogous visual stimuli in area MT and find that these neural responses account for the perceived direction of the stimuli across all stimulus conditions tested.

Shape invariant coding of motion direction in somatosensory cortex.

Invariant representations of stimulus features are thought to play an important role in producing stable percepts of objects. In the present study, we assess the invariance of neural representations of tactile motion direction with respect to other stimulus properties. To this end, we record the responses evoked in individual neurons in somatosensory cortex of primates, including areas 3b, 1, and 2, by three types of motion stimuli, namely scanned bars and dot patterns, and random dot displays, presented to the fingertips of macaque monkeys.

Aging and tactile temporal order.

Although it is generally held that speed of processing declines with age, there have been few studies in which tactile temporal processing has been examined with older subjects. In the present study, temporal order judgments were obtained from a group of younger subjects (n = 28, mean age = 23.5 years) and a group of older subjects (n = 93, mean age = 69.

Convergence of submodality-specific input onto neurons in primary somatosensory cortex.

At the somatosensory periphery, slowly adapting type 1 (SA1) and rapidly adapting (RA) afferents respond very differently to step indentations: SA1 afferents respond throughout the entire stimulus interval (sustained response), whereas RA afferents respond only at stimulus onset (on response) and offset (off response). We recorded the responses of cortical neurons to step indentations and found many neurons in areas 3b and 1 to exhibit properties that are intermediate between these two extremes: These neurons responded during the sustained portion of the stimulus and also at the offset of the stimulus. Several lines of evidence indicate that these neurons, which exist in large proportions even at these early stages of somatosensory cortical processing, receive input from both populations of afferents.

The effects of age on sensory thresholds and temporal gap detection in hearing, vision, and touch.

Differences in sensory function between young (n = 42, 18-31 years old) and older (n = 137, 60-88 years old) adults were examined for auditory, visual, and tactile measures of threshold sensitivity and temporal acuity (gap-detection threshold). For all but one of the psychophysical measures (visual gap detection), multiple measures were obtained at different stimulus frequencies for each modality and task. This resulted in a total of 14 dependent measures, each based on four to six adaptive psychophysical estimates of 75% correct performance.

Discriminating smooth from grooved surfaces: effects of random variations in skin penetration.

The ability to discriminate a smooth surface from a grooved one depends on several variables, including the width of the grooves and the force with which the skin is contacted. It has been hypothesized that this smooth-grooved discrimination with statically presented stimuli is based on intensity cues, namely, the overall difference in perceived intensity between the smooth and grooved surfaces. To test this hypothesis, the perceived intensities of test stimuli were varied on a trial-by-trial basis by varying the depth of penetration the contactor was allowed to travel into the skin.

The representation of stimulus orientation in the early stages of somatosensory processing.

At an early stage of processing, a stimulus is represented as a set of contours. In the representation of form, a critical feature of these local contours is their orientation. In the present study, we investigate the representation of orientation at the somatosensory periphery and in primary somatosensory cortex.

The crossed-hands deficit in tactile temporal-order judgments: the effect of training.

Several recent studies have shown that judgments of temporal order for tactile stimuli presented to the two hands are greatly affected by crossing the hands. The size of the threshold for judging temporal order may be up to four times larger with the hands crossed as compared to the hands uncrossed. The results from these recent studies suggest that with crossed hands, contrary to many situations involving the integration of tactile and proprioceptive information, subjects have difficulty in adjusting their perception of tactile inputs to correspond with the spatial positions of the hands.

A dense array stimulator to generate arbitrary spatio-temporal tactile stimuli.

The generation and presentation of tactile stimuli presents a unique challenge. Unlike vision and audition, in which standard equipment such as monitors and audio systems can be used for most experiments, tactile stimuli and/or stimulators often have to be tailor-made for a given study. Here, we present a novel tactile stimulator designed to present arbitrary spatio-temporal stimuli to the skin.

Visual motion interferes with tactile motion perception.

Previous studies have demonstrated that visual apparent motion can alter the judgment of auditory apparent motion. We investigated the effect of visual apparent motion on judgments of the direction of tactile apparent motion. When visual motion was presented at the same time as, but in a direction opposite to, tactile motion, accuracy in judging the direction of tactile apparent motion was substantially reduced.

Tactile spatial sensitivity and anisotropy.

A gap detection task was examined for its usefulness as a measure of tactile spatial sensitivity and as a measure of anisotropy. In Experiment 1, sensitivity was measured with a gap detection task both with and without a latex glove at three locations on the hand: the fingerpad, fingerbase, and palm. Results showed that sensitivity varied as a function of location and was correlated with changes in the density of innervation of the primary afferent fibers.

The effect of force and conformance on tactile intensive and spatial sensitivity.

The effect of force on intensive and spatial processing was examined with three measures of tactile sensitivity. One of the measures based on intensive cues is the smooth-grooved (SM/GV) task, and the two other measures based on spatial cues are the grating orientation and gap detection tasks. Measures were made at two locations that vary in sensitivity and in the density of innervation of the primary afferent fibers, the right index fingerpad and the palmar surface of the proximal phalanx (fingerbase).

The trajectory effect in intermodal temporal order judgments.

Subjects judged which one of two patterns, a visual or a tactile pattern, had been presented first. The visual and tactile displays were placed in close spatial proximity. The patterns appeared to move across their respective displays.

Ethanol recovery from corn fiber hydrolysate fermentations by pervaporation.

Corn fiber, a byproduct of corn wet milling, is an attractive feedstock for biomass ethanol production. Corn fiber was hydrolyzed by dilute sulfuric acid and neutralized by one of two methods: conventional lime treatment or neutralization by strongly basic anion exchange. The anion exchange neutralized (AEN) hydrolysate contained substantially lower levels of the inhibiting compounds furfural, 5-hydroxymethylfurfural, and acetic acid compared to the lime neutralized hydrolysate.

Proprioceptive perception of phase variability.

Previous work has established that judgments of relative phase variability of 2 visually presented oscillators covary with mean relative phase. Ninety degrees is judged to be more variable than 0 degrees or 180 degrees, independently of the actual level of phase variability. Judged levels of variability also increase at 180 degrees.

The effect of hand position and pattern motion on temporal order judgments.

Subjects made temporal order judgments (TOJs) of tactile stimuli presented to the fingerpads. The subjects judged which one of two locations had been stimulated first. The tactile stimuli were patterns that simulated movement across the fingerpads.

The effect of motion on tactile and visual temporal order judgments.

Four experiments were conducted, three with tactile stimuli and one with visual stimuli, in which subjects made temporal order judgments (TOJs). The tactile stimuli were patterns that moved laterally across the fingerpads. The subject's task was to judge which finger received the pattern first.

Corn-milling pretreatment with anhydrous ammonia.

Exposure to anhydrous ammonia has been suggested as a pretreatment for corn milling. Batches of corn were exposed to ammonia under controlled conditions. The amounts of ammonia absorbed and reacted with the corn were measured.

Relative roles of spatial and intensive cues in the discrimination of spatial tactile stimuli.

Two psychophysical measures of tactile sensitivity--grating-orientation (GO) and smooth-grooved (SG) discrimination--were used to determine tactile spatial acuity with and without an intermediate surface (latex glove) interposed between the contactor and the skin. Measures were made at three locations that varied in sensitivity and in density of innervation of the primary afferent fibers: the index fingerpad (fingertip), palmar surface of the proximal phalanx (fingerbase), and the thenar eminence (palm). Neurophysiological studies have suggested that the density of innervation of SAI fibers is a limiting factor in spatial acuity.

A correction and a comment on Craig and Lyle (2001).

In a recent paper, Craig and Lyle (2001) measured tactile spatial acuity on the palm and compared these results with the results from similar measures on the fingertip. The changes in sensitivity between the two sites appeared to be consistent with estimates of the relative density of innervation between the two sites. Rather than compare their results with changes in the density of innervation, Craig and Lyle should have compared them with changes in the spacing between receptors.

Effect of endogenous triacylglycerol hydrolysates on the mechanical properties of Zein films from ground corn.

Dry-milled yellow corn and freshly ground food and nonfood grade yellow and white hybrid corn kernels were pretreated in a solution of lactic acid and sodium metabisulfite followed by extraction with 70% ethanol. Zein was precipitated from the extract by reducing the ethanol content of the extract to 40%. Lipid associated with the zein isolates was between 15 and 20% and contained mostly endogenous free fatty acids.

The prevalence of tactile motion aftereffects.

The present study examined the prevalence of motion aftereffects (MAEs) in the sense of touch. The effects of two types of apparatuses were tested: a ridged, spinning cylinder and an array of vibrating tactors from the Optacon, a reading aid for the blind. In the first phase of the study, 50 subjects were tested for a total of 200 trials on both stimulators.

Identification of scanned and static tactile patterns.

Most of the studies in which the interactions between target and nontarget spatial patterns have been examined have tested patterns that are generated statically. Static patterns are those in which all the elements of the pattern are presented at the same time and at a fixed location on the skin; however, most tactile information comes to the skin by means of patterns' being scanned across the surface of the skin. In the present study, the interactions between target and nontarget patterns were measured for patterns generated in both the static and the scanned modes.