Effects of glyceryl glucoside on AQP3 expression, barrier function and hydration of human skin.

BACKGROUND/AIM: Aquaporins (AQPs) present in the epidermis are essential hydration-regulating elements controlling cellular water and glycerol transport. In this study, the potential of glyceryl glucoside [GG; alpha-D-glucopyranosyl-alpha-(1->2)-glycerol], an enhanced glycerol derivative, to increase the expression of AQP3 in vitro and ex vivo was evaluated. METHODS: In vitro studies with real-time RT-PCR and FACS measurements were performed to test the induction by GG (3% w/v) of AQP3 mRNA and protein in cultured human keratinocytes. GG-containing formulations were applied topically to volunteer subjects and suction blister biopsies were analyzed to assess whether GG (5%) could penetrate the epidermis of intact skin, and subsequently upregulate AQP3 mRNA expression and improve barrier function. RESULTS: AQP3 mRNA and protein levels were significantly increased in cultured human keratinocytes. In the studies on volunteer subjects, GG significantly increased AQP3 mRNA levels in the skin and reduced transepidermal water loss compared with vehicle-controlled areas. CONCLUSION: GG promotes AQP3 mRNA and protein upregulation and improves skin barrier function, and may thus offer an effective treatment option for dehydrated skin.

Bandwidth requirements for video transmission of american sign language and finger spelling.

Although current video communication schemes use a bandwidth on the order of 1 megahertz, the bandwidth required for video communication of American Sign Language by a simple raster scan is only approximately 20 kilohertz.

Dynamics of automatic and controlled visual attention.

The time course of attention was experimentally observed using two kinds of stimuli: a cue to begin attending or to shift attention, and a stimulus to be attended. Precise measurements of the time course of attention show that it consists of two partially concurrent processes: a fast, effortless, automatic process that records the cue and its neighboring events; and a slower, effortful, controlled process that records the stimulus to be attended and its neighboring events.

The attention operating characteristic: examples from visual search.

Even in the absence of eye movements, we show that subjects are able, upon instruction, to selectively attend to certain kinds of targets and parts of visual arrays. The major mechanism of altering attention is the switching of attention from trial to trial, although intermediate states of shared attention do occur. Attention operating characteristics are shown to be a useful way of describing such data and of assessing the compatibility of tasks to be performed simultaneously.

Extremely rapid visual search: the maximum rate of scanning letters for the presence of a numeral.

Subjects searched a rapid sequence of computer-produced letter arrays for the presence of a numeral in one of the arrays. The subjects' scanning rates were computed from their precentage of correct detections of the location of the numeral. Scanning rates were very high and approximately the same for a wide variety of conditions; the highest scanning rates (125 and 75 letters per second for two subjects) occurred when there were 9 or 16 letters in each of the arrays and when new arrays were presented every 40 to 50 milliseconds. Giving the subject advance knowledge of the numeral to be presented made little difference in the scores.

A signal-to-noise theory of the effects of luminance on picture memory: comment on Loftus.

In studies of picture memory, subjects typically view a sequence of pictures. Their memory is tested either after each picture is presented (short-term recall) or at the end of the sequence (long-term recall). The increase in performance as a function of picture viewing time defines "the rate of information acquisition." Loftus (1985) found that reducing the luminance of a picture reduces the rate at which information is acquired (for both short-term and long-term tests) and, for long viewing times, reduces the total amount of recall. The theory proposed here assumes that both of these effects are consequences of intrinsic noise in the visual system that becomes relatively more prominent as signal (picture luminance or contrast) is reduced. Noise shares a limited capacity channel with signal, and thus noise reduces the rate of information acquisition; noise, as well as signal, occupies space in memory, and thus noise reduces recall performance.

Effects of thiopental on regulatory mechanisms of brain energy metabolism.

After administration of thiopental to artificially ventilated rats, the EEG, cerebral metabolism, intracellular distribution of hexokinase activity and the thiopental concentration in brain was measured. Considering the EEG changes, the time course of thiopental action was divided into an initial stage with increased beta activity and a following second stage with reduced beta activity. The glucose-6-phosphate concentration significantly increased in the first stage and fell again to the control level with the beginning of the second stage. Furthermore, during the second stage the glucose level increased and the hexokinase activity shifted from the mitochondrially bound form to the soluble form. From these results the following conclusions were drawn: Phosphofructokinase activity appeared inhibited only during the initial stage. During the second stage comparable to the stage of surgical anesthesia, thiopental solubilizes bound hexokinase activity inhibiting thereby energy metabolism.

Continuous measurement of visible persistence.

In the synchrony judgment paradigm, observers judge whether a click precedes or follows the onset of a light flash and, on other trials, whether or not a click precedes light termination. The interclick interval defines the duration of visible persistence. An elaboration of this method consists of two phases: In Phase 1, the luminance of a reference stimulus is psychophysically matched to the peak brightness of the test flash. Five luminance values between .1 and 1.0 of the reference stimulus are used subsequently. In Phase 2, a random one of the five reference stimuli, a test flash, and a click are presented; the observer judges whether the click occurred before or after the brightness of test flash reached the reference value (on onset trials) or decayed below it (on termination trials). This method was validated on 3 subjects with test stimuli whose luminance rises and decays slowly in time, and then was used to trace out the precise subjective rise and decay (temporal brightness response function) of brief flashes.

Perceptual delay: a consequence of metacontrast and apparent motion.

Temporal-order judgments were used to demonstrate that a later visual stimulus can delay the perception of an earlier one when the two stimuli together produce the phenomenon of metacontrast or of apparent motion. The perceptual delay is the same for movement and metacontrast and for one or two characters appearing to move or to be masked.

Kinetic depth effect and identification of shape.

We introduce an objective shape-identification task for measuring the kinetic depth effect (KDE). A rigidly rotating surface consisting of hills and valleys on an otherwise flat ground was defined by 300 randomly positioned dots. On each trial, 1 of 53 shapes was presented; the observer's task was to identify the shape and its overall direction of rotation. Identification accuracy was an objective measure, with a low guessing base rate of the observer's perceptual ability to extract 3D structure from 2D motion via KDE. (1) Objective accuracy data were consistent with previously obtained subjective rating judgments of depth and coherence. (2) Along with motion cues, rotating real 3D dot-defined shapes inevitably produced a cue of changing dot density. By shortening dot lifetimes to control dot density, we showed that changing density was neither necessary nor sufficient to account for accuracy; motion alone sufficed. (3) Our shape task was solvable with motion cues from the 6 most relevant locations. We extracted the dots from these locations and used them in a simplified 2D direction-labeling motion task with 6 perceptually flat flow fields. Subjects' performance in the 2D and 3D tasks was equivalent, indicating that the information processing capacity of KDE is not unique. (4) Our proposed structure-from-motion algorithm for the shape task first finds relative minima and maxima of local velocity and then assigns 3D depths proportional to velocity.

Is there feature-based attentional selection in visual search?

A new paradigm combines attentional cuing and rapid serial visual presentation to disentangle the effects of perceptual filtering and location selection. Observers search successive, superimposed arrays, in which feature values are alternated for a target numeral among letters. Two dimensions, size (small, large) and color (red, green) are tested. Selective attention to feature values is jointly manipulated by instructions, presentation probabilities, and payoffs. In Experiment 1, the attended feature provides temporal, not spatial, information; observers show no attentional costs or benefits in response accuracy. In Experiment 2, the attended feature indicates a unique location; observers show consistent attentional costs and benefits. Selective attention to a particular size or color does not cause perceptual exclusion or admission of items containing that feature; it acts by guiding search processes to spatial locations that contain the to-be-attended feature.

Information transfer in iconic memory experiments.

To report letters from briefly exposed letter arrays, subjects must transfer information from a rapidly decaying trace (iconic memory) to more durable storage. In a partial-report paradigm, we systematically varied the proportion (P) of trials with a long cue delay relative to a short cue delay. Practiced subjects used the same transfer strategy independent of P. Data from a partial-report-plus-masking experiment were used to construct a computational model that accurately predicted partial- and whole-report performance with and without masks. Assumptions: Prior to a cue, subjects attend primarily to the middle row of a three-row display, resulting in nonselective transfer. After the cue, they attend only to the cued row. Transfer rate is the product of iconic legibility (which depends on time and retinal location) and attention allocation (which shifts after a cue). Cumulative transfer is limited by the capacity of durable storage.

Ratings of kinetic depth in multidot displays.

Subjects saw kinetic depth displays whose shape (sphere or cylinder) was defined by luminous dots distributed randomly on the surface or in the volume of the object. Subjects rated perceived 3-D depth, rigidity, and coherence. Despite individual differences, all 3 ratings increased with the number of dots. Dots in the volume yielded ratings equal to or greater than surface dots. Each rating varied with 3 of 4 factors (shape, distribution, numerosity, and perspective), but the ratings either between trials or between conditions were often uncorrelated. Object shape affected rigidity but not depth ratings. Veridically perceived polar displays had slightly lower rigidity but higher depth ratings than parallel projection displays. (Reversed polar displays were always grossly nonrigid.) The interaction of ratings and stimulus parameters requires theories and experiments in which different KDE ratings are not treated interchangeably.

Intelligent temporal subsampling of American Sign Language using event boundaries.

How well can a sequence of frames be represented by a subset of the frames? Video sequences of American Sign Language (ASL) were investigated in two modes: dynamic (ordinary video) and static (frames printed side by side on the display). An activity index was used to choose critical frames at event boundaries, times when the difference between successive frames is at a local minimum. Sign intelligibility was measured for 32 experienced ASL signers who viewed individual signs. For full gray-scale dynamic signs activity-index subsampling yielded sequences that were significantly more intelligible than when every mth frame was chosen. This result was even more pronounced for static images. For binary images, the relative advantage of activity subsampling was smaller. We conclude that event boundaries can be defined computationally and that subsampling from event boundaries is better than choosing at regular intervals.

How to study the kinetic depth effect experimentally.

Sperling, Landy, Dosher, and Perkins (1989) proposed an objective 3D shape identification task with 2D artifactual cues removed and with full feedback (FB) to the subjects to measure KDE and to circumvent algorithmically equivalent KDE-alternative computations and artifactual non-KDE processing. (1) The 2D velocity flow-field was necessary and sufficient for true KDE. (2) Only the first-order (Fourier-based) perceptual motion system could solve our task because the second-order (rectifying) system could not simultaneously process more than two locations. (3) To ensure first-order motion processing, KDE tasks must require simultaneous processing at more than two locations. (4) Practice with FB is essential to measure ultimate capacity (aptitude) and, thereby, to enable comparisons with ideal observers. Experiments without FB measure ecological achievement--the ability of subjects to extrapolate their past experience to the current stimuli.

Measuring the spatial frequency selectivity of second-order texture mechanisms.

Recent investigations of texture and motion perception suggest two early filtering stages: an initial stage of selective linear filtering followed by rectification and a second stage of linear filtering. Here we demonstrate that there are differently scaled second-stage filters, and we measure their contrast modulation sensitivity as a function of spatial frequency. Our stimuli are Gabor modulations of a suprathreshold, bandlimited, isotropic carrier noise. The subjects' task is to discriminate between two possible orientations of the Gabor. Carrier noises are filtered into four octave-wide bands, centered at m = 2, 4, 8, and 16 c/deg. The Gabor test signals are w = 0.5, 1, 2, 4 and 8 c/deg. The threshold modulation of the test signal is measured for all 20 combinations of m and w. For each carrier frequency m, the Gabor test frequency w to which subjects are maximally sensitive appears to be approximately 3-4 octaves below m. The consistent m x w interaction suggests that each second-stage spatial filter may be differentially tuned to a particular first-stage spatial frequency. The most sensitive combination is a second-stage filter of 1 c/deg with first-stage inputs of 8-16 c/deg. We conclude that second-order texture perception appears to utilize multiple channels tuned to spatial frequency and orientation, with channels tuned to low modulation frequencies appearing to be best served by carrier frequencies 8 to 16 times higher than the modulations they are tuned to detect.

The functional architecture of human visual motion perception.

UNLABELLED: A powerful paradigm (the pedestal-plus-test display) is combined with several subsidiary paradigms (interocular presentation, stimulus superpositions with varying phases, and attentional manipulations) to determine the functional architecture of visual motion perception: i.e. the nature of the various mechanisms of motion perception and their relations to each other. Three systems are isolated: a first-order system that uses a primitive motion energy computation to extract motion from moving luminance modulations; a second-order system that uses motion energy to extract motion from moving texture-contrast modulations; and a third-order system that tracks features. Pedestal displays exclude feature-tracking and thereby yield pure measures of the first- and second-order systems which are found to be exclusively monocular. Interocular displays exclude the first- and second-order systems and thereby to yield pure measures of feature-tracking. RESULTS: both first- and second-order systems are fast (with temporal frequency cutoff at 12 Hz) and sensitive. Feature tracking operates interocularly almost as well as monocularly. It is slower (cutoff frequency is 3 Hz) and it requires much more stimulus contrast than the first- and second-order systems. Feature tracking is both bottom-up (it computes motion from luminance modulation, texture-contrast modulation, depth modulation, motion modulation, flicker modulation, and from other types of stimuli) and top-down--e.g. attentional instructions can determine the direction of perceived motion.

Object spatial frequencies, retinal spatial frequencies, noise, and the efficiency of letter discrimination.

To determine which spatial frequencies are most effective for letter identification, and whether this is because letters are objectively more discriminable in these frequency bands or because can utilize the information more efficiently, we studied the 26 upper-case letters of English. Six two-octave wide filters were used to produce spatially filtered letters with 2D-mean frequencies ranging from 0.4 to 20 cycles per letter height. Subjects attempted to identify filtered letters in the presence of identically filtered, added Gaussian noise. The percent of correct letter identifications vs s/n (the root-mean-square ratio of signal to noise power) was determined for each band at four viewing distances ranging over 32:1. Object spatial frequency band and s/n determine presence of information in the stimulus; viewing distance determines retinal spatial frequency, and affects only ability to utilize. Viewing distance had no effect upon letter discriminability: object spatial frequency, not retinal spatial frequency, determined discriminability. To determine discrimination efficiency, we compared human discrimination to an ideal discriminator. For our two-octave wide bands, s/n performance of humans and of the ideal detector improved with frequency mainly because linear bandwidth increased as a function of frequency. Relative to the ideal detector, human efficiency was 0 in the lowest frequency bands, reached a maximum of 0.42 at 1.5 cycles per object and dropped to about 0.104 in the highest band. Thus, our subjects best extract upper-case letter information from spatial frequencies of 1.5 cycles per object height, and they can extract it with equal efficiency over a 32:1 range of retinal frequencies, from 0.074 to more than 2.3 cycles per degree of visual angle.

Perception of apparent motion between dissimilar gratings: spatiotemporal properties.

What determines the strength of texture-defined apparent motion perception when the stimulus has no net directional energy in the Fourier domain? In a previous paper [Werkhoven, Sperling & Chubb (1993) Vision Research, 33, 463-485] we demonstrated the counterintuitive finding that the correspondence in spatial frequency and in modulation amplitude between neighboring patches of texture in a spatiotemporal motion path are irrelevant to motion strength. Instead, we found strong support for what we call a single channel or one-dimensional motion computation: a simple nonlinear transformation of the image, followed by standard motion analysis. Here, we further studied the dimensionality of the motion computation in a parameter space that includes texture orientation and stimulus display rate in addition to texture spatial frequency and modulation amplitude. We used ambiguous motion displays in which one motion path, consisting of patches of nonsimilar texture, competes with another motion path comprised entirely of similar texture patches. The data show that motion between dissimilar patches of texture that are orthogonally oriented, have a two octave difference in spatial frequency and differ 50% in modulation amplitude can easily dominate motion between similar patches of texture. A single channel accounts for more than 70% of texture-from-motion strength for the parameter space examined and this channel is invariant for stimulus display rates varying over a four-fold range.

Second-order illusions: Mach bands, Chevreul, and Craik--O'Brien--Cornsweet.

Mach bands, which normally occur at the edges of ramp modulations of luminance, are demonstrated to occur in fullwave stimuli that have ramp modulations of contrast while maintaining constant expected luminance. [The fullwave stimuli are random textures that (1) have a ramp contrast modulation that is exposed by fullwave rectification (e.g. absolute value or square) or by halfwave rectification but (2) have a uniform expected luminance throughout, so the modulation remains hidden without rectification.] Two different textures were used: random pixels and 'Mexican hats'. Stimuli were presented dynamically, with a new instantiation of the texture every 67 msec (this enhances the magnitude of the illusion). Both fullwave Mach-band stimuli exhibit perceptual Mach bands that are decreases or increases in apparent texture contrast with no concomitant change in apparent brightness. The perceived contrast bands in fullwave Mach stimuli and the brightness bands in a conventional luminance Mach-band stimulus have approximately the same magnitude. Chevreul (staircase) illusions in luminance and in fullwave patterns also are found to have approximately similar magnitudes, as do luminance and fullwave Craik--O'Brien--Cornsweet illusions. None of these illusions can be perceived with halfwave textures. These results indicate that second-order (texture) illusions result from fullwave, not halfwave, rectification and involve spatial interactions that are remarkably similar to those in first-order (luminance) processing.