Target Detection Experiment Research Articles

Evaluating tone mapping algorithms for rendering non-pictorial (scientific) high-dynamic-range images

Nine algorithms were implemented to overcome the problem associated with rendering high-dynamic-range scientific imagery to low-dynamic-range display devices. The algorithms were evaluated using two paired-comparison psychophysical experiments judging preference and ”scientific usefulness”. The results showed that, on average, the Zone System algorithm performed best and the Local Color Correction method performed the worst. However, the performance of the algorithms depended on the type of data being visualized. The low correlation between the preference and scientific usefulness judgments ( R 2 = 0.31) indicated that observers used different criteria when judging the image preference versus scientific usefulness. The experiment was repeated using expert observers (radiologists) for an MR scan (Medical image). The results showed that the radiologists used similar criteria as the non-expert observers when judging the usefulness of the rendered images. A target detection experiment was conducted to measure the detectability of an embedded target in the Medical image. The result of the target detection experiment illustrated that the detectability of targets in the image is greatly influenced by the rendering algorithms due to the inherent difference in tone mapping among the algorithms.

Unmixing concurrent EEG-fMRI with parallel independent component analysis

Concurrent event-related EEG-fMRI recordings pick up volume-conducted and hemodynamically convoluted signals from latent neural sources that are spatially and temporally mixed across the brain, i.e. the observed data in both modalities represent multiple, simultaneously active, regionally overlapping neuronal mass responses. This mixing process decreases the sensitivity of voxel-by-voxel prediction of hemodynamic activation by the EEG when multiple sources contribute to either the predictor and/or the response variables. In order to address this problem, we used independent component analysis (ICA) to recover maps from the fMRI and timecourses from the EEG, and matched these components across the modalities by correlating their trial-to-trial modulation. The analysis was implemented as a group-level ICA that extracts a single set of components from the data and directly allows for population inferences about consistently expressed function-relevant spatiotemporal responses. We illustrate the utility of this method by extracting a previously undetected but relevant EEG-fMRI component from a concurrent auditory target detection experiment.

Target detection and driving behaviour measurements in a driving simulator at mesopic light levels

During night-time driving hazardous objects often appear at mesopic light levels, which are typically measured using light meters with a spectral sensitivity that is only valid for photopic light levels. In order to develop suitable mesopic models a target detection experiment was performed in a driving simulator. While subjects drove along a winding road they had to respond to randomly presented circular targets at various eccentricities. The background luminance ranged between 0.01 and 10 cd m(-2), and was either white, yellow, red or blue. The RT, number of missed targets, and driving behaviour were measured. The results show that target detection and driving performance get poorer with decreasing background luminance and increasing eccentricity of the target, in particular for the red colour. At high driving speeds and low luminances subjects tend to neglect left off-axis targets. Luminance calculated with existing reaction-time-based mesopic models fits better to RT data than the widely-used photopic luminance.

Time-frequency analysis of target detection reveals an early interface between bottom-up and top-down processes in the gamma-band

The early visual gamma-band response is an oscillatory signal evoked approximately 100 ms after stimulation. While some studies have found effects of various cognitive processes on this signal, such effects could not be replicated in other studies. Accordingly, some authors have claimed that evoked gamma-band activity reflects merely sensory functions. To resolve these conflicting positions, we conducted a target detection experiment in which the feature that defined the target could be distributed over a large or a small part of the entire stimulus. Only targets covering a larger area of the entire stimulus evoked stronger gamma-band activity than standards although the over-all stimulus size was identical for all stimuli. This increase in evoked activity resulted from stronger oscillatory power and not exclusively from stronger phase-locking. In contrast, N1 and P3 amplitudes were larger for target stimuli irrespective of the distribution of the relevant stimulus feature. These results are consistent with the notion that early gamma-band activity is generated by feature-selective neural assemblies the activity of which can in fact be modulated by top-down processes. This interaction, however, may be only detectable in scalp-recorded EEG if it affects a sufficient number of neural assemblies.

α2‐Noradrenergic effects on ERP and behavioral indices of auditory information processing

Norepinephrine is believed to modulate CNS processing of environmental signals. However, its specific role in stimulus evaluation processes has not been delineated. We examined the effects of the α2 noradrenergic agents, clonidine and yohimbine, on ERP and performance measures of auditory information processing. Ten healthy participants performed a three‐tone target detection experiment, receiving either placebo, 0.2 mg clonidine, or 30 mg yohimbine, in a double‐blind randomized design. The principal locus of action of the noradrenergic agents occurred between 100 and 200 ms poststimulus. P200 latency was sped by yohimbine and slowed by clonidine, and the frontal P3a was shifted in tandem. Components related to target detection (N250 and P3b) were unaffected. The results suggest that norepinephrine modulates CNS mechanisms of selective attention to infrequent stimuli. This may be relevant for patients with schizophrenia, a subset of whom exhibit selective abnormalities of these same ERP components. Our results offer a possible link between these two sets of findings, suggesting that some patients with schizophrenia may have dysfunctional noradrenergic systems.

The effect of practice on location cueing and visual search.

Abstract Location cueing can facilitate response times when target-detection tasks are performed. A target-detection experiment was conducted with inexperienced participants to determine whether or not the magnitude of facilitative location cueing effects would change as a function of practice. Over the course of five test sessions, these effects attenuated. This suggests that practice decreases the influence of location cues on visual search performance and attentional processing. We propose that when participants perform cued visual search experiments and become familiar with potential target locations as a result of extended practice and automaticity, these locations are encoded in spatial memory by an operation called spatial indexing. Resume Le reperage de l'emplacement peut reduire le temps de reaction lors de taches consistant a detecter des cibles. Une experience de detection de cibles a laquelle ont participe des personnes inexperimentees a et menee pour determiner si les effets facilitateurs du reperage de l'emplacement changeaient avec 1'entrainement. Au fil des cinq seances, ces effets se sont attenues, ce qui laisse presumer que 1'entrainement diminue l'influence des reperes sur la recherche visuelle et l'attention necessaire. Nous croyons que, lorsque les participants a des experiences de recherche visuelle avec reperes se sont familiarises avec l'emplacement de cibles potentielles par suite d'un long entrainement et d'une automatisation, l'emplacement de ces cibles est encode dans la memoire spatiale par une operation appelee repertoriage spatial. When target detection tasks are performed, location cues can facilitate or inhibit response times (RTs) depending on whether the cue is a valid indicator of the impending target's location or not (e.g., Posner, Snyder, & Davidson, 1980). A direct or peripheral cue (e.g., a bar-marker, underline, or box), if valid, is typically presented at or near the target's location and, if invalid, at a nontarget location (e.g., Posner, 1980). This technique is sometimes called exogenous cueing. Previous research indicates that, in most cases, when the delay between cue and target onset is 100 ms, valid direct cues have their strongest effect on RTs and, when this cuetarget-onset-asynchrony (CTOA) is increased from 100 to 200 ms, cue effectiveness attenuates (Miller Sr Findlay, 1988; Miller & Rabbitt, 1989; Shepard & Miller, 1989; Weichselgartner & Sperling, 1987). In other words, the facilitative effect of direct cues appears to be transient and to last about 200 ms. If two successive direct cues are presented 200 ms apart at different locations, then the facilitative effect of the first cue not only attenuates, but changes to an inhibitory effect on detection RTs for targets presented at this location 300 ms or more after cue onset (e.g., Posner & Cohen, 1984; Posner, Rafal, Choate, & Vaughan, 1985; Possamai, 1985; Rafal, Egly, & Rhodes, 1994; Tipper, Driver, & Weaver, 1991; Tipper & Weaver, 1998; Tipper, Weaver, & Houghton, 1994; Wright & Richard, 1998). Posner and Cohen (1984) called this effect inhibition-ofreturn and proposed that it occurs to increase visual search efficiency by biasing search away from previously inspected locations and toward novel locations. Thus, the effect of location cues on target-detection RTs appears to change as a function of the delay between cue and target onset. The efficiency of visual search can also increase as observers gain experience with the particular target-detection task at hand. For example, search for a target positioned among distractor items can become more rapid with practice, and can even reach the point at which automatic processes are said to mediate search performance (Czerwinski, Lightfoot, & Shiffrin, 1992; Kahneman & Treisman, 1984; Logan, 1988; Logan & Compton, 1998; Schneider, Dumais, & Shiffrin, 1984). As demonstrated by Treisman, Vieira, and Hayes (1992), an automatic process differs from a low-level, preattentive process in the sense that it becomes more efficient with repeated execution. …

An equivalent sensitivity time control circuit for FM-CW radar

Typical problems for subsurface radar sensing are the existence of strong surface clutter and the difficulty in detection of deep targets due to the attenuation of electromagnetic waves underground. This paper proposes a method of enhancing deep target echo strength for FM-CW radar so that the radar sensitivity is proportional to the range. This technique is similar to the time sensitivity control circuits used for pulse radar, and is based on the differentiation property of the beat signal with respect to time. First, we show that this amplitude compensation approach is feasible both theoretically and experimentally in free space. Next, the validity of this method is confirmed by a subsurface target detection experiment using sandy ground. Finally, a hardware implementation in the FM-CW radar is described. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(6): 1–7, 1997

Comparison of target detection capabilities of the beluga and bottlenose dolphin.

The echolocation detection capabilities of a beluga (Delphinapterus leucas) and an Atlantic bottlenose dolphin (Tursiops truncatus) were directly compared in a target detection experiment. Both animals were trained to detect targets in the presence of masking noise. Targets were stainless-steel, water-filled spheres 7.62 and 22.86 cm in diameter. Target ranges of 16.5 and 40 m were used with the 7.62-cm sphere and 80 m with the 22.86-cm sphere. Masking noise with a flat spectrum from 40-160 kHz was projected from a spherical transducer placed 4 or 5 m, depending on the target distance, from the animal hoop station in line with the target. Target detection performance was determined as a function of masking noise level at each target range. The echo-to-noise ratio (Ee/No)max for the beluga at the 75% correct response threshold was approximately 1.0 dB compared to about 10 dB for the dolphin. The differences of each animal's detection performance across the three ranges were consistent with target strength and transmission loss differences. It is speculated that the difference in performance between the two species may be due to differences in critical bandwidth, signal processing capability, or echolocation strategy.

Measurement of echolocation signals of the Atlantic bottlenose dolphin, Tursiops truncatus Montagu, in open waters.

The echlocation signals of two Atlantic bottlenose dolphins, Tursiops truncatus, were measured while the animals were involved in a target-detection experiment conducted in open waters. The time intervals between successive pulses in a pulse train were found to be highly variable, although the intervals were longer than the time needed for an acoustic signal to travel from the animals to the target and back. Sound pressure levels of the echoranging signals were measured for target ranges of 60, 70, 75, and 80 yds. The peak-to-peak click-source level at 1 yd showed little variation with the target range; the average level was 120.4 dB re 1 μbar for one animal and 122.3 dB for the other. These open-water sound pressure levels are at least 30 dB higher than any click-source levels reported in the literature. Oscilloscope photographs and their Fourier transforms of these high-amplitude clicks are presented. The typical clicks had average durations of 40 μsec, with peak energies between 120 and 130 kHz, much higher than the previously reported energy peaks centered at 35 to 60 kHz.