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The objective of this study was to determine how varying concentrations of the stabilizer, locust bean gum (LBG), and different levels of the emulsifier, mono- and diglycerides (MDGs), influenced fat aggregation and melting characteristics of ice cream. Ice creams were made containing MDGs and LBG singly and in combination at concentrations ranging between 0.0% to 0.14% and 0.0% to 0.23%, respectively. Particle size analysis, conducted on both the mixes and ice cream, and melting rate testing on the ice cream were used to determine fat aggregation. No significant differences (P < 0.05) were found between particle size values for experimental ice cream mixes. However, higher concentrations of both LBG and MDG in the ice creams resulted in values that were larger than the control. This study also found an increase in the particle size values when MDG levels were held constant and LBG amounts were increased in the ice cream. Ice creams with higher concentrations of MDG and LBG together had the greatest difference in the rate of melting than the control. The melting rate decreased with increasing LBG concentrations at constant MDG levels. These results illustrated that fat aggregation may not only be affected by emulsifiers, but that stabilizers may play a role in contributing to the destabilization of fat globules.

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We examined the effect of changing the composition of the carrier on the perception of motion in a drifting contrast envelope. Human observers were required to discriminate the direction of motion of contrast modulations of an underlying carrier as a function of temporal frequency and scaled (carrier) contrast. The carriers were modulations of both color and luminance, defined within a cardinal color space. Random-noise carriers had either binary luminance profiles or flat (gray-scale-white) or 1/f (pink) spectral power functions. Independent variables investigated were the envelope spatial frequency and temporal-drift frequency and the fundamental spatial frequency, color, and temporal-update frequency of the carrier. The results show that observers were able to discriminate correctly the direction of envelope motion for binary-noise carriers at both high (16 Hz) and low (2 Hz) temporal-drift frequencies. Changing the carrier format from binary noise to a flat (gray-scale) or 1/f amplitude profile reduced discrimination performance slightly but only in the high-temporal-frequency condition. Manipulation of the fundamental frequency of the carrier elicited no change in performance at the low temporal frequencies but produced ambiguous or reversed motion at the higher temporal frequencies as soon as the fundamental frequency was higher than the envelope modulation frequency. We found that envelope motion detection was sensitive to the structure of the carrier.

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The data presented in this paper examine the ability of observers to detect a modulation in the contrast of chromatic and luminance gratings as a function of the carrier contrast, duration, and spatial frequency. The nature of the signal underlying this ability is investigated by examining both the paradigm used to make the measurement and the effect of grating masks on performance in the tasks. The results show that observers' ability to discriminate amplitude modulation from an unmodulated carrier is dependent on carrier contrast but only up to approximately 5-8 times carrier-detection threshold. Discrimination is, however, independent of spatial frequency [10-1 cycles per degree (cpd) component-frequency range], carrier color, and, most surprisingly, stimulus duration (1000-30 ms). This set of experiments compliments data from previous papers and assimilates many of the conclusions drawn from this previous data. There is absolutely no evidence for the existence of a distortion product mediating performance under any of the current conditions, and the data seriously question whether the visual system might use such a signal even if it does exist under more extreme conditions than those used here. The evidence suggests that the visual system detects variations in both chromatic and luminance contrast by means of a mechanism operating locally upon the spatial structure of the carrier.

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It has become apparent from recent work that the spatial frequency and orientation content of the first-order (luminance) carrier is very important in determining the properties of a second-order (contrast) modulation of that carrier. In light of this we examined whether there was any evidence for a motion aftereffect in one-dimensional second-order patterns containing only two sinusoidal luminance components: a spatial beat. The stimuli were either 1 cpd luminance sinusoids or 1 cpd luminance beats modulating a carrier sinusoid of 5 cpd. The magnitude of any motion aftereffect, or any directionally specific effect of adaptation, was measured for all combinations of first and second-order test and adapting patterns. Both flickering and non-flickering stimuli were used. The results indicate that a motion aftereffect is only induced by first-order adapting stimuli, and likewise, is only measurable in first-order test stimuli. We find no evidence for any directionally specific effect of adaptation in second-order stimuli, whether the test is counterphased or otherwise. These results apparently conflict with recent reports of a second-order induced motion aftereffect, but are consistent with many other findings which show differences between the detection of motion for first and second-order stimuli. We conclude that the induction of a motion aftereffect for second-order stimuli is not a general result and is critically dependent upon (amongst other things) the local properties of the stimulus, including the spatial frequency and orientation content of the first-order carrier.

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We have tested the independence of red-green chromatic and luminance mechanisms at detection threshold using a method of subthreshold summation. Stimuli were isoluminant red-green gratings and yellow-black luminance gratings that uniquely activate the red-green color and luminance mechanisms, respectively. Stimuli were Gaussian enveloped 0.25, 1 or 4 cpd sinewave gratings, counter-phase flickered at 0, 5 or 9 Hz. The threshold detection of red-green color contrast was measured in the presence of a subthreshold amount of luminance contrast, and vice versa. The results allow a model of linear summation between the color and luminance mechanisms to be rejected, but are well fitted by a model, assuming that these mechanisms are independent but combine to determine detection by probability summation, with a high summation index (median value = 4). We conclude that there are independent red-green chromatic mechanism and luminance detection mechanisms over this range of spatio-temporal conditions.

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The impact of the NHS reforms, and the resulting purchaser-provider split, has refocused attention on the relationship between management and medicine in acute hospitals. It is timely to assess the explanatory power of various theoretical models regarding the management-medicine interface. Argues that this interface is currently rather fluid and that a dynamic and adaptive model is best suited to understanding the way in which doctors and managers develop their relationship within the changing policy context. Two examples illustrate these shifting boundaries.

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It has been reported that equiluminant plaid patterns constructed from component gratings modulated along different axes of a cardinal colour space fail to create a coherent impression of two-dimensional motion [Krauskopf and Farell (1990). Nature, 348, 328-331]. In this paper we assess whether this lack of interaction between cardinal axes is a general finding or is instead dependent upon specific stimulus parameters. Type I and Type II plaids were made from sinusoidal components (1 cpd) each modulated along axes in a cardinal colour space and presented at equivalent perceived contrasts. The spatial angular difference between the two components was varied from 5 to 90 deg whilst keeping the Intersection of Constraints (I.O.C.) solution of the pattern constant. Observers were required to indicate the perceived direction of motion of the pattern in a single interval direction-identification task. We find that: (i) When plaids were made from components modulated along the same cardinal axis, coherent "pattern" motion was perceived at all angular differences. As the angular difference between the components decreased in a Type II plaid, the perceived direction of motion moved closer to the I.O.C. solution and away from that predicted by the vector sum. (ii) A plaid made from components modulated along red-green and blue-yellow cardinal axes (cross-cardinal axis) did not cohere at high angular differences (> 30 deg) but had a perceived direction of the fastest moving component. At lower angular differences, however, pattern motion was detected and approached the I.O.C. solution in much the same way as a same-cardinal axis Type II plaid. (iii) A plaid made from a luminance grating and a cardinal chromatic grating (red-green or blue-yellow) failed to cohere under all conditions, demonstrating that there is no interaction between luminance and chromatic cardinal axes. These results indicate that there are conditions under which red-green and blue-yellow cardinal components interact for the purposes of motion detection.

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The human visual system is much better at analysing the motion of luminance (black and white) patterns than it is at analysing the motion of colour patterns, especially if the pattern is presented very briefly or moves rapidly. We report here that observers reliably distinguish the direction of motion of a colour pattern presented for only 17 milliseconds, provided that the contrast is several times the threshold value (the contrast needed to detect the presence of the pattern). A control experiment, in which a static luminance 'mask' is added to the moving colour pattern, proves that discrimination of the direction of motion of these brief stimuli is colour-specific. The mask drastically impairs discrimination of the direction of motion of a luminance pattern, but it has little effect on a colour pattern. We conclude that the human visual system contains colour-specific motion-detection mechanisms that are capable of analysing very brief signals.

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Second-order Type I and Type II plaids were constructed by combining two random-dot gratings. Each component consisted of a dynamic random-dot field, the contrast of which was modulated by a drifting sinusoidal grating. Orienting the two components suitably and interleaving at 120 Hz allowed us to produce a two-dimensional plaid pattern made from one-dimensional second-order components. The perceived direction of motion of both Type I and Type II plaids was measured as a function of stimulus duration. Type I plaids had a perceived direction close to the intersection of constraints/vector sum solution (which only coincide for these patterns) at all durations. Type II plaids had a perceived direction that moved away from the vector sum and toward the intersection of constraints solution as the duration of presentation increased. These results are similar in form to those found for plaids made from first-order (luminance-defined) components [Yo & Wilson (1992), Vision Research, 32, 135-147]. This suggests that a delay which operates specifically on second-order signals cannot be the sole cause for the change in perceived direction of Type II plaids made from first-order components [Wilson, Ferrera & Yo (1992), Visual Neuroscience, 9, 79-97].

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It is commonly assumed that the ability to discriminate velocity in a stimulus directly reflects the properties of the underlying directionally-selective mechanism. The results presented here show that this assumption is not always correct. Speed discrimination tasks over a range of base velocities were carried out for luminance gratings, chromatic gratings and contrast (beat) gratings of equivalent periodicity and contrasts. At low contrasts (0.5 log units above detection threshold), speed discrimination in luminance gratings was at least twice as good (when expressed as a Weber fraction), than in either chromatic gratings or beats. This is similar to the situation seen for tasks of direction discrimination using these stimuli [e.g. Cropper and Derrington (1990) Perception, 19, A31]. When the stimulus contrasts were increased to 1.5 log units above detection threshold, the ability to discriminate speed in both chromatic and beat stimuli improved to a performance level comparable to that shown for luminance gratings at all contrasts. This effect is not seen for tasks of direction discrimination when the same increase in stimulus contrast has little effect on the lower threshold of motion (LTM) measured for beat patterns. These results indicate that the ability to discriminate velocity in a stimulus does not necessarily directly reflect the characteristics of the ability to discriminate the direction of motion of that stimulus.

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This paper measures the minimum velocity required to discriminate the direction of motion (the lower threshold of motion--LTM) for patterns which consisted of spatial variations in luminance, chromaticity or luminance contrast in an attempt to distinguish between the underlying directionally-selective mechanisms. The characteristics of these patterns can be defined as first-order/Fourier stimuli (luminance and chromatic gratings) or second-order/non-Fourier stimuli (contrast gratings or "beats"). Measurements for each pattern were made at durations ranging from 0.015 to 0.96 sec and at contrasts of 0.5 log units above detection threshold and 1.5 log units above the threshold for detecting the stationary pattern. Observers were able to discriminate the direction of motion in luminance gratings and high contrast chromatic gratings at all durations above 0.015 sec. The direction of motion of beats and low contrast chromatic gratings was indiscriminable until they had been presented for at least 0.12 sec. This was taken to indicate the existence of a fast-acting and a slow-acting system dealing with the first- and second-order patterns respectively. When defined on this basis, the chromatic stimulus acts as a first-order (luminance) pattern at high contrasts and a second-order (beat) pattern at low contrasts.

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The mechanism and route of clearance of intestinal alkaline phosphatase from plasma have been studied in rats to define the magnitude of hepatic extraction and biliary excretion of the enzyme. Plasma clearance, tissue distribution, and biliary excretion of enzyme were followed after intravenous administration of physiological amounts of 125I-labeled rat intestinal alkaline phosphatase. The plasma disappearance curve was biphasic; the initial phase was rapid, during which 50% of injected enzyme was selectively extracted by the liver over 5 min. Less than 4% of total hepatic radioactivity was excreted into bile over 80 min; this was shown by chromatographic analysis to be degraded enzyme only. Rapid clearance of enzyme could be significantly slowed by injection of large amounts of mannan or N-acetylglucosamine-bovine serum albumin, but not by desialylated fetuin, demonstrating that clearance was probably mediated by mannose/N-acetylglucosamine-specific receptors. It is concluded that, under physiological conditions, rat plasma intestinal alkaline phosphatase is rapidly cleared from the circulation by the liver. However, biliary excretion of undergraded enzyme is negligible, and a physiologically significant enterohepatic circulation seems most unlikely.

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