A detector of sonic and ultrasonic vocalizations with frequency readout

An electronic apparatus to detect vocalizations between 4 and 50 kHz and to provide frequency readout is described. A frequency-to-voltage converter changes vocalizations to their analog. A peak-and-hold circuit retains and gates the maximal value of this analog voltage while it is accessed by a chart recorder or computer. Provision is made to lock out noise by inhibiting the device’s response to all signals lower than those associated with a selectable cutoff frequency. In preliminary tests of the apparatus, vocal signals of two rats in a common cage were recorded while the animals were subjected to a brief, intermittent bout of faradic shock to the feet. All recorded vocalizations occurred at frequencies below 26 kHz.     

Time,change, and motion: The effects of stimulus movement on temporal perception

The effects of stimulus motion on time perception were examined in five experiments. Subjects judged the durations (6–18 sec) of a series of computer-generated visual displays comprised of varying numbers of simple geometrical forms. In Experiment 1, subjects reproduced the duration of displays consisting of stationary or moving (at 20 cm/sec) stimulus figures. In Experiment 2, subjects reproduced the durations of stimuli that were either stationary, moving slowly (at 10 cm/sec), or moving fast (at 30 cm/sec). In Experiment 3, subjects used the production method to generate specified durations for stationary, slow, and fast displays. In Experiments 4 and 5, subjects reproduced the duration of stimuli that moved at speeds ranging from 0 to 45 cm/sec. Each experiment showed that stimulus motion lengthened perceived time. In general, faster speeds lengthened perceived time to a greater degree than slower speeds. Varying the number of stimuli appearing in the displays had only limited effects on time judgments. Other findings indicated that shorter intervals tended to be overestimated and longer intervals underestimated (Vierordt’s law), an effect which applied to both stationary and moving stimuli. The results support a change model of perceived time, which maintains that intervals associated with more changes are perceived to be longer than intervals with fewer changes.     

Apparent depth with retinal image motion of expansion and contraction yoked to head movement

The two main questions addressed in this study were (a) what effect does yoking the relative expansion and contraction (EC) of retinal images to forward and backward head movements have on the resultant magnitude and stability of perceived depth, and (b) how does this relative EC image motion interact with the depth cues of motion parallax? Relative EC image motion was produced by moving a small CCD camera toward and away from the stimulus, two random-dot surfaces separated in depth, in synchrony with the observers' forward and backward head movements. Observers viewed the stimuli monocularly, on a helmet-mounted display, while moving their heads at various velocities, including zero velocity. The results showed that (a) the magnitude of perceived depth was smaller with smaller head velocities (< 10 cm s-1), including the zero-head-velocity condition, than with a larger velocity (10 cm s-1), and (b) perceived depth, when motion parallax and the EC image motion cues were simultaneously presented, is equal to the greater of the two possible perceived depths produced from either of these two cues alone. The results suggested the role of nonvisual information of self-motion on perceiving depth.     

Eye movement prediction and variability on natural video data sets

We here study the predictability of eye movements when viewing high-resolution natural videos. We use three recently published gaze data sets that contain a wide range of footage, from scenes of almost still-life character to professionally made, fast-paced advertisements and movie trailers. Inter-subject gaze variability differs significantly between data sets, with variability being lowest for the professional movies. We then evaluate three state-of-the-art saliency models on these data sets. A model that is based on the invariants of the structure tensor and that combines very generic, sparse video representations with machine learning techniques outperforms the two reference models; performance is further improved for two data sets when the model is extended to a perceptually inspired colour space. Finally, a combined analysis of gaze variability and predictability shows that eye movements on the professionally made movies are the most coherent (due to implicit gaze-guidance strategies of the movie directors), yet the least predictable (presumably due to the frequent cuts). Our results highlight the need for standardized benchmarks to comparatively evaluate eye movement prediction algorithms.     

Infants' recognition of a face revealed through motion: contribution of internal facial movement and head movement

The experiment reported here explores 3-month-old infants' ability to recognize a human face from a specific motion pattern lacking static facial features. A woman's face was covered with black makeup and numerous white triangles. It was videotaped while the woman was pretending to interact with a baby. A soft rubber mask was prepared likewise and was videotaped while being moved and deformed by hand. In one condition, the face or mask showed facial movement only, while in a second condition there was internal movement plus head movement. The two stimuli were presented either in upright or in upside-down orientation. Results of 48 subjects indicate that the discrimination of face and mask was easier when the stimuli were presented upright. The absence of head movements did not influence the discriminability. These results suggest that 3-month-old infants organize the moving triangles on the face in the upright orientation into a coherent facelike structure.     

Methods of correcting correlations for indirect restriction of range with non-interval data

A derivation is presented for correcting correlations for indirect restriction of range when correlations between one selection variable and non-interval measures are involved. Following a systematic investigation of special cases, formulas are given for practical application in validation work. Procedures for the case with several selection variables are briefly discussed.This study was initiated when the author was with the Institute of Military Psychology, Sweden.     

Neural substrates of individual differences in human fear learning: Evidence from concurrent fMRI, fear-potentiated startle, and US-expectancy data

To provide insight into individual differences in fear learning, we examined the emotional and cognitive expressions of discriminative fear conditioning in direct relation to its neural substrates. Contrary to previous behavioral-neural (fMRI) research on fear learning--in which the emotional expression of fear was generally indexed by skin conductance--we used fear-potentiated startle, a more reliable and specific index of fear. While we obtained concurrent fear-potentiated startle, neuroimaging (fMRI), and US-expectancy data, healthy participants underwent a fear-conditioning paradigm in which one of two conditioned stimuli (CS(+) but not CS(-)) was paired with a shock (unconditioned stimulus [US]). Fear learning was evident from the differential expressions of fear (CS(+) > CS(-)) at both the behavioral level (startle potentiation and US expectancy) and the neural level (in amygdala, anterior cingulate cortex, hippocampus, and insula). We examined individual differences in discriminative fear conditioning by classifying participants (as conditionable vs. unconditionable) according to whether they showed successful differential startle potentiation. This revealed that the individual differences in the emotional expression of discriminative fear learning (startle potentiation) were reflected in differential amygdala activation, regardless of the cognitive expression of fear learning (CS-US contingency or hippocampal activation). Our study provides the first evidence for the potential of examining startle potentiation in concurrent fMRI research on fear learning.     

An improved algorithm for automatic detection of saccades in eye movement data and for calculating saccade parameters

This analysis of time series of eye movements is a saccade-detection algorithm that is based on an earlier algorithm. It achieves substantial improvements by using an adaptive-threshold model instead of fixed thresholds and using the eye-movement acceleration signal. This has four advantages: (1) Adaptive thresholds are calculated automatically from the preceding acceleration data for detecting the beginning of a saccade, and thresholds are modified during the saccade. (2) The monotonicity of the position signal during the saccade, together with the acceleration with respect to the thresholds, is used to reliably determine the end of the saccade. (3) This allows differentiation between saccades following the main-sequence and non-main-sequence saccades. (4) Artifacts of various kinds can be detected and eliminated. The algorithm is demonstrated by applying it to human eye movement data (obtained by EOG) recorded during driving a car. A second demonstration of the algorithm detects microsleep episodes in eye movement data.     

An experiment on the theory of visual motion perception

Two classes of theories of motion perception were studied: correlation and gradient models (in the sense of D. Marr). Random-dot kinematograms with a shifted square were presented to subjects, and the 80% threshold for detection of correct direction of movement was determined. Correlation models predict scale invariance, that is, a constant shift measured in units of texture elements of the translated pattern in spite of a geometric magnification. This was refuted for all subjects. The increase of the recognizable translation with the area of the translated form was verified except for the patterns with the largest texture elements (8 minutes of arc). This prediction, however, is not very specific for competing theories. Gradient models are not yet fully specified, and they contain some free parameters. They cannot be tested strictly, but there exist reasonable numerical parameter values by which our data can be satisfactorily explained.     

Visual feedback,movement learning and the representation of movement

Two experiments on movement learning are reported where the orientation of a visual curve on a graphics terminal, defining a relatively complex arm movement, was either orthogonal to or compatible with the direction of the required movement. In addition, individual differences in spatial orientation and visualization abilities were correlated with motor performance. Results in both experiments showed that equivalent amounts of learning occurred in the two visual conditions. However, during transfer trials to the opposite condition, virtually no transfer occurred for the compatible group when they performed in the orthogonal condition whereas there was tranfer when the orthogonal group performed in the compatible condition. The results supported the idea that very early in learning the orthogonal orientation of visual curve promoted the development of an orientation processing stage which facilitated transrer performance of the orthogonal group. Integrating these results with the past literature on movement learning led to the notion that the orientation information processing stage can be considered a cognitive system that interacts with the image of the act. Finally, contrary to expectations, spatial orientation ability failed to account for any performance while spatial visualization ability moderately correlated with performance.     

Affective reactivity of language symptoms, startle responding, and inhibition in schizophrenia

The speech of some schizophrenia patients becomes markedly more disordered when negative affect is aroused. The authors tested associations between affective reactivity of speech and responsiveness and inhibition on an acoustic startle task in a sample of 27 outpatients. Patients whose language was reactive to negative affect showed significantly higher initial startle amplitudes than those whose language was not reactive. However, they also showed greater habituation to repeated startle stimuli over trials, even after differences in initial amplitudes were controlled statistically. These findings suggest that affective reactivity of speech is associated with higher initial startle responsiveness but also with greater habituation and, conversely, that patients who are relatively nonreactive to excitatory affective and sensory stimuli are also less reactive to inhibitory input.     

An EEG alpha-detection,feedback stimulation,and data analysis system

A two-channel general-purpose EEG alpha-detection system is described, along with the associated computer hardware and software. A specific application for the study of the human orienting response using alpha-contingent visual stimulation is presented. Limitations are discussed.