Human Psychophysics Research Articles

Range effects in successive discrimination.

In two sets of experiments we examined pigeons' discrimination performance with a visual flicker-rate continuum, using a conventional successive discrimination procedure. In the first experiment, responses during the intermediate stimulus value were never reinforced, while responses during stimuli on either end of the continuum were reinforced periodically. In the second experiment, responses during stimuli from one end of the continuum were never reinforced, while responses during stimuli from the other end of the continuum were reinforced periodically. Results from both experiments show that discrimination between unchanged positive and negative stimulus values is a function of the range over which the total stimulus set varies. These range effects are comparable to effects found in absolute judgment tasks in human and animal psychophysics. In addition, the range effects reported here are not due to channel capacity, but may depend instead on variability in judgment criteria.

Color cell groups in foveal striate cortex of the behaving macaque.

Color-tuning curves were obtained for 218 cells in the foveal striate cortex of behaving macaques. Each cell was tested with its optimal spatial stimulus. Test colors (14 interference filters, 4 Wratten filters, and white) were matched for human photopic luminosity and presented at luminance levels sufficient to induce vigorous responding from most cells. One hundred eighty-four cells were selected for further analysis on the basis of a color-tuning index. Of these, 130 with tuning curves that correlated well (0.9 or better) with other tuning curves were studied in detail. Individual cells were found with peak responses to every color tested. Sixty-three tuning curves fell into the six largest cross-correlation groups, containing 15, 14, 12, 9, 7, and 6 cells, with mean tuning-curve peaks at 450, 656, 656, 506, 577, and 506 nm, respectively. Cross-correlation groups having the same peak location (656 nm, 506 nm) were distinguishable on the basis of tuning-curve width. Response patterns, cone input estimates, and comparison with human psychophysics suggest that two of these cell groups function as an opponent pair processing the colors red and green. Two other cell groups process the colors blue and yellow but show less well-developed opponency. Microdrive depth readings, correlated with histological lesion sites, show these "red," "green," "blue," and "yellow" cells to be most common in layer 4 of the striate cortex.

Model of human visual-motion sensing.

We propose a model of how humans sense the velocity of moving images. The model exploits constraints provided by human psychophysics, notably that motion-sensing elements appear tuned for two-dimensional spatial frequency, and by the frequency spectrum of a moving image, namely, that its support lies in the plane in which the temporal frequency equals the dot product of the spatial frequency and the image velocity. The first stage of the model is a set of spatial-frequency-tuned, direction-selective linear sensors. The temporal frequency of the response of each sensor is shown to encode the component of the image velocity in the sensor direction. At the second stage, these components are resolved in order to measure the velocity of image motion at each of a number of spatial locations and spatial frequencies. The model has been applied to several illustrative examples, including apparent motion, coherent gratings, and natural image sequences. The model agrees qualitatively with human perception.

Lecture to American College of Radiology

Image processing applied to medicine is more constrained than in other fields. Lacking means of verification, as is often the case, it is difficult to judge what constitutes a success or how the ideal image should look. Most successful processing efforts to date have been directed at correcting distortions introduced by shortcomings in the imaging equipment itself or methods for filling in missing data sets. Some important headway has been made in processing which is directed at providing a better match to human visual psychophysics particularly in matrix images. The greatest future opportunities appear to lie in image integration of several different imaging modalities of the same body part and utilization of a priori information as a factor in image formation.

Design Criteria for Safer Manual Lifting by Men and Women

Simplified design criteria are provided for two-handed, manual lifting by standing men and women, without selective assignment of personnel to specific material handling tasks. Based on a 1981 NIOSH report, application of these criteria requires no knowledge of human anatomy, anthropometry, biomechanics, psychophysics, muscle fatigue, cardiovascular capacity, or metabolic endurance. A person who can read and use simple graphs can quickly determine the maximum weight of a lifted object. The information needed is the horizontal grasp distance and the initial grasp height and lift distance of the object, plus the frequency and duration of lifting.

Velocity sensitivity of areas 17 and 18 of the cat

Velocity sensitivity of areas 17 and 18 of the cat has been evaluated by preparing neuronal velocity-response (VR) curves in paralyzed and anaesthetized cats. VR curves suggest two possible mechanisms for neuronal coding of stimulus velocity as well as criterion for distinguishing between cells involved in analysis of stationary or moving objects. VR curves differ between cortical areas and with retinal eccentricity. Neurones with larger receptive fields (RFs) become, on the average, sensitive to faster velocities. Parallels with human psychophysics are pointed out as support of the suggestion that the present results are relevant for our insights in human motion perception.

Discrimination between trunk and head rotation: A study comparing neuronal data from the cat with human psychophysics

Kinesthetic information from labyrinthine and neck receptors is required for reflex control and conscious perception of posture and movement. This study considers (1) the neuronal responses to horizontal labyrinthine and neck stimulation and their interaction both in the anterior suprasylvian (AS) cortex and in the vestibular nuclei (VN) of cats, and (2) human turning sensation related to these stimuli. Convergence of labyrinthine (L) and neck (N) input of comparable sensitivity was found in 80% of the AS neurons and in only 27% of the VN neurons. At both sites, the on-direction of L-responses as well as N-responses was either to the ipsilateral or to the contralateral side (type I and type II responses, respectively). When combining the two stimuli during head rotation, the two inputs could be synergistic (same on-direction) or antagonistic (opposite on-directions). Their interaction consisted of either an additive or subtractive summation leading to enhanced or depressed interaction responses. These interaction patterns are compatible with the subtractive and additive mechanisms which have been proposed to be essential for the stabilisation of the trunk and of the head, respectively. The psychophysical experiments showed that human turning sensations depend on the part of the body to which they are referred. Subjects taking the trunk as reference, reported similar turning sensations during both labyrinthine and neck stimulation, and weak or no turning sensation during head rotation. This suggests an antagonistic interaction of the two inputs. In subjects taking the head as reference, neck stimulation induced an illusionary sensation of head turning. Its direction was such that it would be synergistic with the vestibularly induced sensation of head turning during isolated head rotation. Thus, there appear to exist parallels between the basic operations performed by neurons in cat and by human subjects during labyrinthine-neck interactions.

Models of stimulus uncertainty in motion perception.

A model is proposed to account for the loss in visibility of moving targets that occurs when an observer is uncertain about the target's direction of motion. The model's key features are an array of directionally selective visual mechanisms and a rule governing the mechanisms from which an observer will derive sensory data. In response to uncertainty about two possible directions of motion, the observer is assumed to use a mechanism whose peak sensitivity is to a direction midway between the two possible directions. Seven experiments, using both reaction time and forced-choice data, demonstrate the predictive advantages of this midway model over competing single-band and multiple-band models. Additionally, the experiments reveal several new properties of human motion perception: (a) Direction and velocity information have orthogonal representations in the visual system; (b) although motion sensitivity does not vary with direction, the precision with which small changes in direction can be recognized does, reflecting differential breadth of tuning for directionally selective mechanisms sensitive to various directions; and (c) motion-analyzing mechanisms are broadly tuned for direction as well as speed. Human psychophysics provides extensive evidence for the existence of visual mechanisms tuned to different directions of motion. Converging on this point are data from a variety of paradigms including selective adaptation (Sekuler & Ganz, 1963), subthreshold summation (Levinson & Sekuler, 1975), and aftereffects (Keck, Palella, & Pantle, 1976). In addition, we recently used a masking procedure to define the direction sensitivity profiles of these mechanisms (Ball & Sekuler, 1979). In general, these studies tell us how much information is potentially available in motion-sensit ive visual elements under ideal conditions. But they tell us little about the use to which that information can be put under nonideal conditions outside the laboratory.

Human psychophysics: Functional interpretation for contrast sensitivity versus spatial frequency curve

The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings in addition to the suprathreshold phenomenon of matching sinusoidal gratings of different spatial frequencies. This offers a unifying interpretation for why, at threshold conditions, the high spatial frequency portion of the image is blurred as severely by the nervous system as it is by the optics (e.g. Campbell and Green, 1965) while in extreme suprathreshold conditions the nervous system effectively deblurs the image (e.g. Georgeson and Sullivan, 1975; Kulikowski, 1976). These conclusions do not necessitate a highly specific form of visual processing such as Fourier channeling.

Masking, De Lange curves and integration time as revealed by the electroretinogram of a tree shrew (Tupaia chinensis)

Dynamical characteristics of the electroretinogram (ERG) of a tree shrew were measured. Since this animal has a cone dominated receptor population (95%) comparison to human photopic vision is obvious. The light source was chosen to stimulate the red cones of this deuteranopic animal predominantly. Masking experiments displayed a reasonable correspondence to human foveal psychophysics. De Lange curves and CFF values revealed a maximum sensitivity at 15-20 HZ, which is higher than is found for human vision. A secondary maximum was observed in the De Lange curves at high adaptation levels, which is possibly due to interactions of the ERG components. The dependency of integration time on adaptation level appeared to be similar to known data of human psychophysics and electrophysiological data from Limulus receptor cells.

Compatibility between psychophysical and physiological measurements of aural combination tones.

Neural studies of combination-tone (CT) responses in the eighth nerve and antroventral cochlear nucleus of anesthetized cats give evidence of stimuluslike intracochlear CT's with a similar amplitude spectrum as inferred from human psychophysics. An unsolved problem raised in these studies is the gross discrepency between the phase of CT's measured psychophysically and neurally. It is unknown whether incompatibility lies in the cochleas or the criteria for measuring CT's in the different experiments. New psychophysical experiments were developed to clarify this issue. Secondary CT's (SCT) were generated by the interaction between a primary cubic CT (CTT) and a third tone in the stimulus. The SCT measured by cancellation exhibits similar properties to those of a CT generated by the comparable two-tone stimulus. The SCT is eliminated when the CCT is cancelled. These findings support the view that CT's exist in the cochlea as spatially distinct, stimuluslike excitations, and that CT excitations are eliminated by psychophysical cancellation. The SCT phase provides a measure of the CCT phase without requiring direct cancellation of the CCT. Phase measurements by the new indirect and older direct methods imply that the CT phase may be constant with changing sound level of the primary stimulus as found in the neural studies; these measurements also reveal nonlinear phase effects not found in neural studies. The new data suggest that the CT phase discrepancy may be caused by a real difference between the nonlinear mechanisms in the alert humans and anesthetized cats, and provide new constraints for clarifying this issue through further study.

An APL program for calculating signal detection indices

Since Green and Swets' Signal Detection Theory and Psychophysics (1966), numerous books and articles have developed statistical decision or signal detection theory (SOT), for example, Egan (1975), Egan and Clarke (1966), Green and Swets (1966jI974), McNicol (1972), and Swets (1973). In addition, the. model has been applied to diverse areas of research: an~al as well as human psychophysics, memory, personality, learning, medicine, and behavioral pharmacology (Aiken, 1969; Appel & Dykstra, 1977; Lloyd & Appel, 1976; Price, 1966;Swets, 1969; Terman, 1970). In brief, SOT attempts to differentiate statistically between effects on discrimination of variables related to physical properties of the stimulus (sensitivity) and effects of variables related to characteristics of the response (criterion or bias). In this attempt, numerous parametric as well as nonparametric indices of both sensitivity and bias estimation have been developed (Dusoir, 1975; Green & Swets, 1966jI974;Grier, 1971; Hodos, 1970; Pollack, 1970; Pollack & Hsieh, 1969; Pollack & Norman, 1964). Of these, the most familiar parametric measures are d' (sensitivity) and (3 or In{3 (bias). The most familiar nonparametric measures are A' or P(I) (sensitivity) and B'H (bias). In applications of SOT, a yes-no procedure is often employed. In this paradigm a subject reports either that a stimulus has (R+) or has not (R-) occurred, given that the stimulus has (S+) or has not (S-) been presented. All possible outcomes can be represented as four relative frequencies, that is, HIT = fr(R+jS+), MISS = fr(R-jS+), False Alarm (FA) = fr(R+jS-), and Correct Rejection (CR) = fr(R-jS-). From these frequencies, conditioned probabilities, that is, p(R+/S+) and p(R+jS-), can be determined. When sample size is not too large or the number of observations is limited, indices of both sensitivity and bias can be calculated in a reasonable amount of time; moreover, tables of both d' and {3 are available for some, but not all, conditional probabilities (Freeman, 1973). A serious problem arises when parametric indices are used and the data a!e inconsistent with the assumptions of the model, that IS, Thurstone's case V of underlying normal distribution

THE EFFECTS OF VARYING THE DISTRIBUTION OF GENERALIZATION STIMULI WITHIN A CONSTANT RANGE UPON THE BISECTION OF A SOUND‐INTENSITY INTERVAL BY RATS1

Two male, albino rats were trained on a two-valued, self-paced, discrete-trials auditory discrimination. In the presence of a high-intensity stimulus (90 decibels SPL, 4 kiloHertz), response A was reinforced; in the presence of a low-intensity stimulus (50 decibels SPL, 4 kiloHertz), response B was reinforced. When discrimination performance was asymptotic, stimuli intermediate in intensity were presented with the training stimuli in a maintained generalization paradigm. Generalization gradients were derived from the relative frequencies of response A in the presence of each stimulus. A relative frequency of 0.50 was then determined and used as the bisection point of the intensity interval defined by the 90- and 50-decibel stimuli. The bisection point varied with the distribution of the stimuli presented in generalization. This effect was similar to context effects seen in human psychophysics.

Auditory detection and optimal response biases

Rats were trained to detect a signal consisting of an increment in the intensity of a random noise. The procedure was analogous to the yes-no method of human psychophysics, in that one response was defined as correct and reinforced with brain stimulation if the signal was presented, and another response was correct and reinforced if the noise alone was presented. Incorrect responses produced periods of time-out. Bias functions showing how the animals’ response probabilities varied as the signal intensity was reduced were obtained in two ways. In Experiment 1, the probability of presenting the signal was varied over four values between 0.4 and 0.6. In Experiment 2, the number of brain stimulations consequent upon a correct response in the presence of the signal was varied over four values between 3:1 and 1:2. Differences of 0.10 and 0.05 in the signal probability, and unit differences in the ratio of brain stimulations, resulted in distinctly different bias functions. Accuracy of detection increased with the signal intensity, and was independent of the animals’ response biases. When the signal probability was varied, the animals optimized the number of correct trials, and hence the number of brain stimulations obtained. When the ratio of brain stimulations was varied, the animals compromised between optimizing the number of correct trials and optimizing the number of brain stimulations obtained.

Detection of increments in noise intensity by monkeys.

Monkeys were trained to detect 100-msec increments in the intensity of continuous white noise. A response on one of two bars was reinforced with some probability if it conformed to the presence or absence of the increment on that trial. Stimulus parameters of background intensity, increment size, and probability of increment presentation were varied, and response probabilities and latencies were recorded. The task was analogous to the "yes-no" task used in human psychophysics. Data analysis within the context of signal-detection theory revealed response biasing toward one bar or the other to be related to the probability of increment presentation, whereas sensitivity depended on the combination of increment size and background noise intensity. Weber's law was found to hold for a large range of background intensities in that the sensitivity to relative intensity increments varied little. Performance was compared to that of an ideal observer that uses samples of the envelope of the noise waveform on which to base its responses.

Summation of pain produced in different anatomical regions*

Unescapable shock was administered to rats in a spatial preference task through pairs of electrodes implanted subcutaneously near the neck and tail. The animals were permitted to choose between shock through both pairs of electrodes or through one pair by crossing from one side of a cage to the other. Rats preferred shock in two locations to an equal amount in one location. The results indicate that summation of pain is greater when stimuli are added in the same rather than in different places. When two aversive stimuli, such as noise and shock, are administered to rats, the aversive properties of the two stimuli summate (Campbell, 1968). However, results from human psychophysics indicate that summation is the exception, rather than the rule, when stimuli interact. For instance, vibrotactile stimulation

Detection of brief tones in noise by rats.

Two rats were trained to detect brief 8000-Hz tones centered in a one-third octave band of noise. The procedure was analogous to the yes-no method of human psychophysics in that one response was defined as correct and reinforced if the tone were present in the noise, and another response was correct and reinforced if the tone were absent. The percentage of correct responses was determined principally by the energy in the tone for the range of durations studied (75 to 600 msec): if the tone's duration were halved, for example, its power had to be doubled to keep the percentage of correct responses about the same. The ratio of the energy in the tone to the power per cycle of the noise needed to maintain 75% correct responses was about 36 db for one animal and 41 db for the other. Although the two responses were similar, and their consequences equal, biases in responding were sometimes observed.

BINAURAL INTERACTION IN THE ACCESSORY SUPERIOR-OLIVARY NUCLEUS OF THE CAT.

Acoustic clicks were presented through earphones to the two ears of anesthetized cats, and the electrical response activity of single nerve cells in the accessory nucleus of the superior olive was studied. Stimulus parameters investigated included interaural time difference, interaural intensity difference, and average intensity. Attention was concentrated on cells that were excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. The experimental results are incorporated into van Bergeijk's model for binaural interaction, for which it is postulated that localization judgments are obtained on the basis of a comparison of the amounts of response activity in the two accessory nuclei. The model yields predictions that are in agreement with results from human psychophysics. The model predicts that the virtual image should be lateralized toward the side receiving prior or more intense stimulation. A time-intensity trading relationship that is in agreement with results from “centering” experiments is derived. The model predicts minimum detectable changes in interaural time difference of 5–10 μsec and minimum detectable changes in interaural intensity difference of 0.1–0.5 dB.

Binaural Interaction in the Accessory Superior-Olivary Nucleus of the Cat

In an effort to understand the neural encoding of binaurally presented stimuli, clicks were presented through earphones to the two ears of anesthetized cats and the electrical response activity of single cells in the accessory superior-olivary nucleus was studied. Stimulus parameters investigated included interaural time difference, interaural intensity difference, and average intensity. Attention was focused on cells that were excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. A model is suggested in which localization judgments are obtained on the basis of activity in the accessory nuclei. In the model, the position of the virtual image is determined by a comparison of the amount of response activity in the two accessory nuclei. Incorporation of empirical data into the model yields predictions that are in agreement with results from human psychophysics. The model predicts that the virtual image should be localized toward the side receiving more-intense or prior stimulation. A time-intensity trading relationship that is in agreement with results from “centering” experiments is derived. The model predicts minimum detectable changes in interaural time difference of 5–10 μsec and minimum detectable changes in interaural intensity difference of 0.1–0.5 dB. [This work was supported in part by the U. S. Army, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; and in part by the National Science Foundation (grant G-16526) and the National Institutes of Health, U. S. Department of Health, Education, and Welfare (grant MH-04737-03).]