Engineering topics

Null, Cynthia H.

Publications and source records attributed to Null, Cynthia H..

90 records · Page 5

NASA NTRS1995

Analysis of the Trial-By-Trial Correlation Between Eye Movement and Perceptual Responses to Moving Plaids

We have previously shown that windowing a drifting plaid with an asymmetric spatial Gaussian produces systematic biases of similar magnitude in both the perceived direction of motion and the direction of the eye movement response. To further investigate this, we simultaneously measured the pyschophysical and eye-movement responses (with an ISCAN RK426 IR tracker)to drifting plaids in a direction discrimination task. Three observers were instructed to track a plaid (Type I 90 deg.; TF = 4 Hz, SF = 0.6 c/d; windowed by a circular spatial gaussian) and to respond whether the motion was to the right or left of pure vertical. Three plaid directions were presented (-2, 0, 2 deg. with respect to straight down), so there was uncertainty in the perceptual judgements. This enabled us to examine the trial-by-trial relationship between the eye movements and psychophysical responses. The eye-movement direction was computed to be the slope of the best fitting line to the initial 300 ms of saccade-free tracking (near open-loop). Again, we found the mean psychophysical and oculomotor responses were correlated. The mean percentages of rightward responses were 6, 27, 87%, and the mean normalized eye-movement directions were -1.5, 0, and 1.0 deg. for the -2, 0, and 2 deg. stimuli respectively. We also computed the trial-by-trial correlation by performing an SOC analysis. The mean correlations were 0.52, 0.66, and 0.67 for our three observers. Because of eye-tracker measurement noise, the above results are lower limits on the actual correlation. These results support the view that the oculomotor and perceptual system share common motion inputs.

Beutter, Brent R.↗

NASA NTRS1995

The Relative Contribution of Interaural Time and Magnitude Cues to Dynamic Sound Localization

This paper presents preliminary data from a study examining the relative contribution of interaural time differences (ITDs) and interaural level differences (ILDs) to the localization of virtual sound sources both with and without head motion. The listeners' task was to estimate the apparent direction and distance of virtual sources (broadband noise) presented over headphones. Stimuli were synthesized from minimum phase representations of nonindividualized directional transfer functions; binaural magnitude spectra were derived from the minimum phase estimates and ITDs were represented as a pure delay. During dynamic conditions, listeners were encouraged to move their heads; the position of the listener's head was tracked and the stimuli were synthesized in real time using a Convolvotron to simulate a stationary external sound source. ILDs and ITDs were either correctly or incorrectly correlated with head motion: (1) both ILDs and ITDs correctly correlated, (2) ILDs correct, ITD fixed at 0 deg azimuth and 0 deg elevation, (3) ITDs correct, ILDs fixed at 0 deg, 0 deg. Similar conditions were run for static conditions except that none of the cues changed with head motion. The data indicated that, compared to static conditions, head movements helped listeners to resolve confusions primarily when ILDs were correctly correlated, although a smaller effect was also seen for correct ITDs. Together with the results for static conditions, the data suggest that localization tends to be dominated by the cue that is most reliable or consistent, when reliability is defined by consistency over time as well as across frequency bands.

Wenzel, Elizabeth M.↗

NASA NTRS1995

Spatial and Spatial Frequency Spreads Of Masking: Measurements and a Contrast-Gain-Control Model

Masked pattern detection is affected by the mask's proximity to the target in both the spatial and the spatial frequency domains. We measured contrast thresholds for detection of a Gabor patch centered in a sample of static band-pass noise with a central noise-free aperture. To examine spatial spread, target and mask frequency were identical, at either 2, 4, or 8 cycles/degree (cpd), and the radius of the aperture was 0, 1/2 or 1 cycle of the noise band's center frequency. The results suggest that the spatial spread of masking is scale invariant, with the largest radius producing little masking. To examine spatial frequency spread, a radius of 0 (no aperture) was used with all pairings of 2,4, and 8 cpd for target and mask. The results suggest that masking is asymmetrical over log frequency: 8 cpd noise masks a 2 cpd target, but 2 cpd noise does not mask an 8 cpd target. We have used these results to calibrate a model of contrast-gain-control.

Solomon, J. A.↗

NASA NTRS1995

Binocular Convergence and Errors in Judged Distance While Using Head-mounted See-through Displays

Previous observations have shown that optical superposition of a physical backdrops at the judged depth of a stereoscopic virtual image moves the judged depth closer to the observer. This effect was more pronounced for slowly moving physical backdrops and was not enhanced when the virtual image was rendered as a flat shaded solid object rather than a open wire-frame. Since this change in rendering making the virtual image more completely occlude the backdrop did not effect its judged depth and since the motion of the backdrop which would have attracted visual attention and binocular convergence did Increase its perceptual displacement, it was concluded that the change In Judged depth was not due to the perceived occlusion. Rather it was concluded to be due to an increase in binocular convergence. An experimental test of this hypothesis using a unobtrusive nonius technique to detect absolute and relative convergence has confirmed the presence of convergence correlated with the magnitude of the change in judged position of this virtual Image. The practical implications of this cause are demonstrated by a second study using monocular, biocular and stereoscopic viewing conditions and the consequences for the design of head-mounted see-through displays for near work are discussed.

Ellis, Stephen R.↗

NASA NTRS1995

The Barberplaid illusion: Even Perceived Plaid Motion is Biased by Asymmetric Apertures

Our results show that the perceived direction of motion of plaids windowed by asymmetric spatial Gaussians is biased toward the long axis of the window. The bias increases as the relative angle between the plaid motion and the window increases, peaks at a relative angle of about 40 degrees, and then decreases. The peak bias was 14 degrees for a spatial frequency of 0.6 cpd and a window aspect ratio of 4.0. The biases increase as the window is elongated and decrease as the component spatial frequency increases. We tested the predictions of several models of human motion processing (cross correlation, motion energy, intersection of constraints, and vector sum), and show that none of these can predict our data. These results suggest that spatial integration of motion signals plays a crucial role in the perception of plaid motion.

Beutter, Brent↗

NASA NTRS1995

Reflexive OKN is Biased Like Perception

The classic "barber-pole illusion" demonstrates how the perceived motion of an ambiguous stimulus is influenced by the shape of the viewing aperture: the motion is preferentially seen in the direction of the long axis of the aperture. We have previously reported (ARVO 94) that we are able to continuously vary the strength of this effect by varying the aspect ratio of the window. In the present study we examined the motion of the eyes while subjects viewed such stimuli in an attempt to discover whether the eye movement control system performs the same computation underlying the perceptual judgments.

Mulligan, Jeffrey B.↗

NASA NTRS1995

A comparison of Image Quality Models and Metrics Predicting Object Detection

Many models and metrics for image quality predict image discriminability, the visibility of the difference between a pair of images. Some image quality applications, such as the quality of imaging radar displays, are concerned with object detection and recognition. Object detection involves looking for one of a large set of object sub-images in a large set of background images and has been approached from this general point of view. We find that discrimination models and metrics can predict the relative detectability of objects in different images, suggesting that these simpler models may be useful in some object detection and recognition applications. Here we compare three alternative measures of image discrimination, a multiple frequency channel model, a single filter model, and RMS error.

Rohaly, Ann Marie↗

NASA NTRS1995

Image Discrimination Models With Stochastic Channel Selection

Many models of human image processing feature a large fixed number of channels representing cortical units varying in spatial position (visual field direction and eccentricity) and spatial frequency (radial frequency and orientation). The values of these parameters are usually sampled at fixed values selected to ensure adequate overlap considering the bandwidth and/or spread parameters, which are usually fixed. Even high levels of overlap does not always ensure that the performance of the model will vary smoothly with image translation or scale changes. Physiological measurements of bandwidth and/or spread parameters result in a broad distribution of estimated parameter values and the prediction of some psychophysical results are facilitated by the assumption that these parameters also take on a range of values. Selecting a sample of channels from a continuum of channels rather than using a fixed set can make model performance vary smoothly with changes in image position, scale, and orientation. It also facilitates the addition of spatial inhomogeneity, nonlinear feature channels, and focus of attention to channel models.

Ahumada, Albert J., Jr.↗

NASA NTRS1995

Depth Cue Integration in an Active Control Paradigm

Numerous models of depth cue integration have been proposed. Of particular interest is how the visual system processes discrepent cues, as might arise when viewing synthetic displays. A powerful paradigm for examining this integration process can be adapted from manual control research. This methodology introduces independent disturbances in the candidate cues, then performs spectral analysis of subjects' resulting motoric responses (e.g., depth matching). We will describe this technique and present initial findings.

Kaiser, Mary K.↗

NASA NTRS1994

Spatial Attention Enhances Perceptual Processing of Single-Element Displays

Shiu and Pashler (1993) reported that precueing masked, single-element displays had negligible effects on identification accuracy. They argued that spatial attention does not actually enhance stimulus perceptibility, but only reduces decision noise. Alternatively, such negative results may arise if cues are sub-optimal, or if masks place an insufficient premium on timely deployment of attention. We report results showing that valid cueing enhances processing of even single-element displays. Spatial attention does indeed enhance perceptual processes.

Bacon, William↗

NASA NTRS1994

A Perceptual Repetition Blindness Effect

Before concluding Repetition Blindness is a perceptual phenomenon, alternative explanations based on memory retrieval problems and report bias must be rejected. Memory problems were minimized by requiring a judgment about only a single briefly displayed field. Bias and sensitivity effects were empirically measured with an ROC-curve analysis method based on confidence ratings. Results from five experiments support the hypothesis that Repetition Blindness can be a perceptual phenomenon.

Hochhaus, Larry↗

NASA NTRS1994

Perceptual Repetition Blindness Effects

The phenomenon of repetition blindness (RB) may reveal a new limitation on human perceptual processing. Recently, however, researchers have attributed RB to post-perceptual processes such as memory retrieval and/or reporting biases. The standard rapid serial visual presentation (RSVP) paradigm used in most RB studies is, indeed, open to such objections. Here we investigate RB using a "single-frame" paradigm introduced by Johnston and Hale (1984) in which memory demands are minimal. Subjects made only a single judgement about whether one masked target word was the same or different than a post-target probe. Confidence ratings permitted use of signal detection methods to assess sensitivity and bias effects. In the critical condition for RB a precue of the post-target word was provided prior to the target stimulus (identity precue), so that the required judgement amounted to whether the target did or did not repeat the precue word. In control treatments, the precue was either an unrelated word or a dummy.

Hochhaus, Larry↗

NASA NTRS1994

Attentional Capture Can Depend on Search Mode

We have previously reported that an irrelevant singleton in one color does not capture attention when the target is defined by a singleton in a different color. Here, we show that when subjects are uncertain of the target color, capture occurs even when distractors and targets differ in color. The effects of target certainty on capture are explained in terms of the contingent involuntary orienting hypothesis of Folk, Remington, and Johnston (1992).

Remington, Roger W.↗

NASA NTRS1994

Virtual Acoustic Displays for Teleconferencing: Intelligibility Advantage for "Telephone Grade" Audio

Speech intelligibility was evaluated using a virtual acoustic ("3-D audio") display using the method specified by ANSI. Ten subjects were evaluated with stimuli either unfiltered or low-pass filtered at 4 kHz. Results show virtual acoustic techniques are advantageous for both full-bandwidth (44.1 kHz srate) and low (8 kHz srate) bandwidth "telephone-grade" teleconferencing systems.

Begault, Durand R.↗

NASA NTRS1994

Extracting Depth From Motion Parallax in Real-World and Synthetic Displays

In psychophysical studies on human sensitivity to visual motion parallax (MP), the use of computer displays is pervasive. However, a number of potential problems are associated with such displays: cue conflicts arise when observers accommodate to the screen surface, and observer head and body movements are often not reflected in the displays. We investigated observers' sensitivity to depth information in MP (slant, depth order, relative depth) using various real-world displays and their computer-generated analogs. Angle judgments of real-world stimuli were consistently superior to judgments that were based on computer-generated stimuli. Similar results were found for perceived depth order and relative depth. Perceptual competence of observers tends to be underestimated in research that is based on computer generated displays. Such findings cannot be generalized to more realistic viewing situations.

Hecht, Heiko↗

NASA NTRS1994

Contrast Gain Control Model Fits Masking Data

We studied the fit of a contrast gain control model to data of Foley (JOSA 1994), consisting of thresholds for a Gabor patch masked by gratings of various orientations, or by compounds of two orientations. Our general model includes models of Foley and Teo & Heeger (IEEE 1994). Our specific model used a bank of Gabor filters with octave bandwidths at 8 orientations. Excitatory and inhibitory nonlinearities were power functions with exponents of 2.4 and 2. Inhibitory pooling was broad in orientation, but narrow in spatial frequency and space. Minkowski pooling used an exponent of 4. All of the data for observer KMF were well fit by the model. We have developed a contrast gain control model that fits masking data. Unlike Foley's, our model accepts images as inputs. Unlike Teo & Heeger's, our model did not require multiple channels for different dynamic ranges.

Watson, Andrew B.↗

NASA NTRS1994

Image Discrimination Models Predict Object Detection in Natural Backgrounds

Object detection involves looking for one of a large set of object sub-images in a large set of background images. Image discrimination models only predict the probability that an observer will detect a difference between two images. In a recent study based on only six different images, we found that discrimination models can predict the relative detectability of objects in those images, suggesting that these simpler models may be useful in some object detection applications. Here we replicate this result using a new, larger set of images. Fifteen images of a vehicle in an other-wise natural setting were altered to remove the vehicle and mixed with the original image in a proportion chosen to make the target neither perfectly recognizable nor unrecognizable. The target was also rotated about a vertical axis through its center and mixed with the background. Sixteen observers rated these 30 target images and the 15 background-only images for the presence of a vehicle. The likelihoods of the observer responses were computed from a Thurstone scaling model with the assumption that the detectabilities are proportional to the predictions of an image discrimination model. Three image discrimination models were used: a cortex transform model, a single channel model with a contrast sensitivity function filter, and the Root-Mean-Square (RMS) difference of the digital target and background-only images. As in the previous study, the cortex transform model performed best; the RMS difference predictor was second best; and last, but still a reasonable predictor, was the single channel model. Image discrimination models can predict the relative detectabilities of objects in natural backgrounds.

Ahumada, Albert J., Jr.↗

NASA NTRS1993

A white paper: NASA virtual environment research, applications, and technology

Research support for Virtual Environment technology development has been a part of NASA's human factors research program since 1985. Under the auspices of the Office of Aeronautics and Space Technology (OAST), initial funding was provided to the Aerospace Human Factors Research Division, Ames Research Center, which resulted in the origination of this technology. Since 1985, other Centers have begun using and developing this technology. At each research and space flight center, NASA missions have been major drivers of the technology. This White Paper was the joint effort of all the Centers which have been involved in the development of technology and its applications to their unique missions. Appendix A is the list of those who have worked to prepare the document, directed by Dr. Cynthia H. Null, Ames Research Center, and Dr. James P. Jenkins, NASA Headquarters. This White Paper describes the technology and its applications in NASA Centers (Chapters 1, 2 and 3), the potential roles it can take in NASA (Chapters 4 and 5), and a roadmap of the next 5 years (FY 1994-1998). The audience for this White Paper consists of managers, engineers, scientists and the general public with an interest in Virtual Environment technology. Those who read the paper will determine whether this roadmap, or others, are to be followed.

Null, Cynthia H.↗