Image capture: simulation of sensor responses from hyperspectral images.

This paper describes the design and performance of an image capture simulator. The general model underlying the simulator assumes that the image capture device contains multiple classes of sensors with different spectral sensitivities and that each sensor responds in a known way to irradiance over most of its operating range. The input to the simulator is a set of narrow-band images of the scene taken with a custom-designed hyperspectral camera system. The parameters for the simulator are the number of sensor classes, the sensor spectral sensitivities, the noise statistics and number of quantization levels for each sensor class, the spatial arrangement of the sensors and the exposure duration. The output of the simulator is the raw image data that would have been acquired by the simulated image capture device. To test the simulator, we acquired images of the same scene both with the hyperspectral camera and with a calibrated Kodak DCS-200 digital color camera. We used the simulator to predict the DCS-200 output from the hyperspectral data. The agreement between simulated and acquired images validated the image capture response model and our simulator implementation. We believe the simulator will provide a useful tool for understanding the effect of varying the design parameters of an image capture device.

Identification of iodinated proteins in cultured thyrocytes and their possible significance for thyroid hormone formation.

The thyroid gland is known to generate the iodinated hormones T3 and T4 from the prohormone thyroglobulin. In this report we examined whether polypeptides other than thyroglobulin are iodinated and hormonogenic in thyrocytes and the prerequisites for their iodination. In primary cultures of porcine thyrocytes, a substantial portion of organified radioiodine was incorporated into cellular proteins other than thyroglobulin. Some of these were identified by immunoprecipitation. They included proteins of the extracellular matrix, plasma membrane proteins, and lysosomal enzymes, which follow in part a secretion and recapture pathway. All of these proteins come into contact with the iodinating system of thyrocytes located on the apical plasma membrane and possess iodination consensus sequences. Immunoprecipitation with T3- or T4-specific antibodies showed that thyroid hormones were detectable only within thyroglobulin. This was confirmed by an analysis of the iodoamino acids of thyroglobulin, cathepsin-D (representing a secretory protein), and aminopeptidase-N (a membrane-integrated protein) by two-dimensional TLC, which revealed the presence of T3 and T4 only within the polypeptide chain of thyroglobulin. These results indicate that iodoproteins other than thyroglobulin do not participate in the generation of thyroid hormones in situ.

Determinants of the perception of sagittal motion.

This study examines the change in the perceived distance of an object in three-dimensional space when the object and/or the observer's head is moved along the line of sight (sagittal motion) as a function of the perceived absolute (egocentric) distance of the object and the perceived motion of the head. To analyze the processes involved, two situations, labeled A and B, were used in four experiments. In Situation A, the observer was stationary and the perceived motion of the object was measured as the object was moved toward and away from the observer. In Situation B, the same visual information regarding the changing perceived egocentric distance between the observer and object was provided as in Situation A, but part or all of the change in visual egocentric distance was produced by the sagittal motion of the observer's head. A comparison of the perceived motion of the object in the two situations was used to measure the compensation in the perception of the motion of the object as a result of the head motion. Compensation was often clearly incomplete, and errors were often made in the perception of the motion of the stimulus object. A theory is proposed, which identifies the relation between the changes in the perceived egocentric distance of the object and the tandem motion of the object resulting from the perceived motion of the head to be the significant factor in the perception of the sagittal motion of the stimulus object in Situation B.

An "exhaustive" search for tasks that fall between the choice and simple reactions.

An experimental search was made for reaction time (RT) tasks that require the processing operation of stimulus discrimination or response selection, but not both. The existence of such a task would allow the subtractive determination of the mean duration of the separate operations. Each of the three reactions that historically have been represented as possessing only one of the two operations was subjected to empirical testing. None of them met the most basic requirements. Donders' (1868/1969) contingent (c) reaction and Taylor's (1966) selection (b')reaction were not reliably faster than a compatible choice (b) reaction. Wundt's (1880) discrimination (d) reaction was not sensitive to difficulty of discrimination. The possibility is suggested that stimulus discrimination and response selection in the choice reaction are inseparable operations. The present negative results emphasize the importance of establishing validity of any use of the subtraction method through appropriate experimental methods. Some parallels of the compatibility issue are found in experiments in which RT is used as a measure of the duration of programming operations.

Absence of compensation and reasoning-like processes in the perception of orientation in depth.

When errors are present in the perceived depth between the parts of a physically stationary object, the object appears to rotate as the head is moved laterally (Gogel, 1980). This illusory rotation has been attributed either to compensation (Wallach, 1985, 1987) or to inferential-like processes (Rock, 1983). Alternatively, the perceived distances of and directions to the parts of the object are sufficient to explain the illusory perceived orientations and perceived rotations of the stimulus. This was examined in three experiments. In Experiment 1, a perceived illusory orientation of a stimulus object extended in depth was produced by misleading binocular disparity and was measured at two different lateral positions of the head under two conditions. In the static condition, the head was stationary at different times at each of the two measurement positions of the head. In the dynamic condition, continuous motion of the head occurred between these two positions. In Experiment 2, static and dynamic conditions of illusory stimulus orientation were observed with the head stationary. In Experiment 3, a perspective illusion instead of binocular disparity produced the errors in perceived depth. In no experiment did the perceived orientation of the object differ for the static and dynamic conditions. In the absence of head motion, neither compensatory nor inferential-like processes were available. It is concluded that these processes are not needed to explain either illusory or nonillusory perceptions of the orientation or rotation of stimuli viewed with a laterally moving head.

Eye fixation and attention as modifiers of perceived distance.

An error in the perceived distance of a physically stationary object results in an apparent horizontal motion of the object if the head is moved horizontally. Procedures have been developed to use this apparent motion to measure the apparent distance of the object. Research also has indicated that the apparent distance of an object will tend to be displaced toward the distance at which the eyes are fixated. In the present study head-motion procedures were used to measure the effect of eye fixation and attention upon the apparent distance of a point of light in two experiments. Substantial errors in perceived distance occurred in the predicted direction as a function of fixation distance. Attending to an object at a distance other than the distance of the fixated point of light had a much less effect upon the apparent distance of the point. It is concluded that the apparent conomitant motion which occurs in a variety of situations as a function of the distance of fixation indicates that substantial errors in perceived distance are common in most environments.