Pulsed fluoroscopy (hereafter called pulsed) at reduced acquisition rates, typically 15 acq/s (pulsed‐15), is proposed to reduce x‐ray dose in interventional procedures. However, since the human visual system (HVS) acts as a temporal low‐pass filter that interacts with such acquisitions, the proper dose for pulsed must be obtained in perception experiments. We determine the dose for low‐frame‐rate pulsed that gives visualization equivalent to that of conventional 30 acq/s fluoroscopy, hereafter called continuous. Computer‐generated phantoms are used. They consist of stationary, low‐contrast disks on a flat background containing Poisson noise that mimics quantum noise in fluoroscopy. Image sequences are displayed on the video tachistoscope, a device with considerable display flexibility. Three experimental paradigms are used. (1) In a paired‐comparison study, pulsed and continuous are displayed side‐by‐side on the same monitor, and the visibility of a contrast detail phantom is compared. (2) Using this same display, subjects record the minimally detectable disk contrast (the min‐contrast measurement). (3) In a four‐alternative forced‐choice experiment, a disk is placed in one of four positions, and the subject determines the position of the disk. The methods are complementary—the forced‐choice experiment properly eliminates the subjectivity of the observer threshold while the paired‐comparison study is much more time efficient. With regard to pulsed and continuous comparisons, remarkable similarity is found between the supra‐threshold experiments (1 and 2) and the detectability experiment (3); i.e., the average absolute differences in the equivalent‐perception dose as determined by the three measures is approximately 3%. No difference is found between interlaced and noninterlaced display. A relatively small dependence of dose savings on disk size is found with larger disks giving increased dose savings. Average dose savings of 22%, 38%, and 49% are found for pulsed‐15, pulsed‐10, and pulsed‐7.5, respectively.

1. Measurements were made in four normal human subjects of the accuracy of saccades to remembered locations of targets that were flashed on a 20 x 30 deg random dot display that was either stationary or moving horizontally and sinusoidally at +/-9 deg at 0.3 Hz. During the interval between the target flash and the memory-guided saccade, the "memory period" (1.4 s), subjects either fixated a stationary spot or pursued a spot moving vertically sinusoidally at +/-9 deg at 0.3 Hz. 2. When saccades were made toward the location of targets previously flashed on a stationary background as subjects fixated the stationary spot, median saccadic error was 0.93 deg horizontally and 1.1 deg vertically. These errors were greater than for saccades to visible targets, which had median values of 0.59 deg horizontally and 0.60 deg vertically. 3. When targets were flashed as subjects smoothly pursued a spot that moved vertically across the stationary background, median saccadic error was 1.1 deg horizontally and 1.2 deg vertically, thus being of similar accuracy to when targets were flashed during fixation. In addition, the vertical component of the memory-guided saccade was much more closely correlated with the "spatial error" than with the "retinal error"; this indicated that, when programming the saccade, the brain had taken into account eye movements that occurred during the memory period. 4. When saccades were made to targets flashed during attempted fixation of a stationary spot on a horizontally moving background, a condition that produces a weak Duncker-type illusion of horizontal movement of the primary target, median saccadic error increased horizontally to 3.2 deg but was 1.1 deg vertically. 5. When targets were flashed as subjects smoothly pursued a spot that moved vertically on the horizontally moving background, a condition that induces a strong illusion of diagonal target motion, median saccadic error was 4.0 deg horizontally and 1.5 deg vertically; thus the horizontal error was greater than under any other experimental condition. 6. In most trials, the initial saccade to the remembered target was followed by additional saccades while the subject was still in darkness. These secondary saccades, which were executed in the absence of visual feedback, brought the eye closer to the target location. During paradigms involving horizontal background movement, these corrections were more prominent horizontally than vertically. 7. Further measurements were made in two subjects to determine whether inaccuracy of memory-guided saccades, in the horizontal plane, was due to mislocalization at the time that the target flashed, misrepresentation of the trajectory of the pursuit eye movement during the memory period, or both. 8. The magnitude of the saccadic error, both with and without corrections made in darkness, was mislocalized by approximately 30% of the displacement of the background at the time that the target flashed. The magnitude of the saccadic error also was influenced by net movement of the background during the memory...

Wedeveloped an adaptive forced-choice method whereby reference and test presentations were alternated in order to minimize effects from variables such as subject attention level. In our demonstration example of an X-rayfluoroscopy perception study, we measured detectability of low-contrast objects in noisy image sequences and determined X-raydose levels for equivalent detectability of identical contrasts for a new test acquisition method (fluoroscopy at 15 acq/sec) as compared with a reference (conventional fluoroscopy at 30acq/sec). In preliminary experiments, we found a dose savings with the test method. We derived parameter uncertainties for the adaptive procedure and demonstrated their applicability with Monte Carlo simulations. Repeated experiments on a single subject demonstrated reduced standard errors due to the reduction of day-to-day variations. It is believed that the method can be applied in a variety of situations in which one needs to compare perception measurements.We have developed a new experimental method that addresses issues in human perception studies. First, a subject's response can vary due to fatigue, a lapse in attention, or possible physiological changes. Kahneman (1973) discussed the importance of attention in perception experiments, indicating that attention may affect the sensory mechanism as well as the decision mechanism. Taylor (1967) observed variation in performance from one day to the next, and others (Hall, 1981;Madigan & Williams, 1987) reported variations within single experiments. This variation complicates comparison of results. For example, in our experiments in medical X-ray fluoroscopy, we compared new test acquisition methods with an established reference technique. Some of the effects that we wished to measure are comparable to day-to-day variations, and our solution was to alternate reference and test presentations over a time scale of seconds and obtain responses under identical conditions. Second, variability between subjects also presents a dilemma. For an independent variable such as image contrast, many trial-and-error presentations are required to arrive at display conditions that match the floor and ceiling responses of all subjects. This problem is well known, and adaptive techniques can solve the problem (

Pulsed fluoroscopy at reduced frame rates can be used to lower x-ray dose with equivalent detection (hereafter called equivalent perception) of low-contrast, stationary objects. Experimentally average dose savings of 22%, 38%, and 49%, for pulsed fluoroscopy at 15, 10, and 7.5 acquisitions per second, respectively, are documented. Dose savings depend on object size, with fewer savings for smaller objects. To explain these data, we extend the framework of an ideal observer with three models for the spatiotemporal response of the human visual system (HVS). They are model 1, separable; model 2, nonseparable; and model 3, nonseparable with internal observer noise. With no free parameters, model 1 predicts the average dose savings within a 3% difference but does not describe the effect of object size. Models 2 and 3 explain the influence of size, and model 3, with a single free parameter, fits the measurements best. Perception of pulsed fluoroscopy is thus well described in terms of spatiotemporal processing by the HVS.

Multiple forms of a symbol-digit substitution task were used to provide a componential analysis of age differences in coding task performance. The results demonstrated age differences in feature encoding, memory, and visual search. A 2nd experiment was conducted with young adults to investigate a sensory deficit as a locus of age differences. The spatial contrast sensitivity deficit of older adults was simulated on forms by applying a digital filter. Persons in the age-simulated contrast condition performed worse than those in the normal contrast condition. The stimulus degradation effect was linked to visual search speed. The study illustrates the utility of componential analysis and offers direct support for the hypothesis that sensory deficits affect performance on tasks used to assess intelligence.