Evaluation of a dynamical model of speech perception

Previous work (Tuller, Case, Ding, & Kelso, 1994) has revealed signature properties of nonlinear dynamical systems in how people categorize speech sounds. The data were modeled by using a two-well potential function that deformed with stimulus properties and was sensitive to context. Here we evaluate one prediction of the model--namely, that the rate of change of the potential's slope should increase when the category is repeatedly perceived. Judged goodness of category membership was used as an index of the slope of the potential. Stimuli from a "say"-"stay" continuum were presented with gap duration changing sequentially throughout the range from 0 to 76 to 0 msec, or from 76 to 0 to 76 msec. Subjects identified each token as either "say" or "stay" and rated how good an exemplar it was of the identified category. As predicted, the same physical stimulus presented at the end of a sequence was judged a better exemplar of the category than was the identical stimulus presented at the beginning of the sequence. In contrast, stimuli presented twice near the middle of a sequence with few (or no) stimuli between them, as well as stimuli presented with an intervening random set, showed no such differences. These results confirm the hypothesis of a context-sensitive dynamical representation underlying speech.     

The effect of timing and spatial separation on the velocity of auditory apparent motion

Previously, it was shown that the minimum conditions for the illusion of auditory apparent motion (AAM) depend on stimulus timing but not spatial separation. In the present experiment, the effects of stimulus timing and source separation on the perceived velocity of AAM were examined. Eight listeners estimated the velocity, duration, and distance traveled of AAM, using a no-modulus, magnitude estimation procedure. Four burst durations (25, 50, 100, and 300 msec), 10 stimulus onset asynchronies (SOAs; 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 msec) and two separations (10 degrees and 40 degrees) were tested. Perceived velocity estimates were related to the total duration (burst duration + SOA) of the stimulus sequence. The effect of separation on velocity was extremely small but statistically significant. These results are similar to those obtained previously on the minimum conditions for AAM. Duration estimates were related only to total duration, but separation estimates were related to both separation and total duration. These results suggest that velocity is possibly a primary dimension of AAM that is independent of source separation.     

Semantic processing of non-attended visual information.

In 2 experiments, with 28 university students, reaction time (RT) to name 1 of 2 rows of letter material was measured. The reported row was always a word. In Exp I, the nonreported row contained either a word semantically related to the reported word, a nonassociated word, or a nonword. Nonwords were not used in Exp II. Attentional selectivity was varied by presenting a report cue either 250 msec prior to display onset or 250 msec after display onset. RT was faster when the report cue preceded the display, indicating that this cue induced selective attention. In both the selective and nonselective conditions, RT to name the target word was faster when the nonreported row contained a word associated with the target than when it contained a nonassociated word. However, this facilitation of RT produced by associated nonreported words was greater under the nonselective condition. While semantic information was extracted from both nonattended and attended visual material a larger semantic interaction occurred when attention was directed to both rows of a visual display. Results also indicate that the presence of nonwords influenced the strategy used to analyze a visual display. (French summary) (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The interaction between stereoscopic and luminance motion

An interaction in apparent motion between perceived three-dimensional forms defined by stereopsis and local luminous elements is reported. Vertical stripes of cyclopean square gratings were simulated by random-dot stereograms. Alternation of two-frame stereograms whose phases differed by 90 deg caused two kinds of percepts, planes' motion in depth (first-order stereoscopic motion, first-order SM) or lateral motion of gratings (higher-order stereoscopic motion, higher-order SM). Experiment 1 explored the conditions under which higher-order SM frequently arose, as opposed to local luminance-based in-depth motion (first-order SM). The results show that, when the spatial arrangements of two-frame random dots were correlated, higher-order SM dominated for long ISI conditions (ISI > 73 msec). When they were uncorrelated, higher-order SM dominated even under zero ISI conditions. Subjects reported that, when higher-order SM was seen, dots were attached to the surfaces of the moving cyclopean figure (motion capture). Experiment 2 tested which factor caused the domination of higher-order SM under uncorrelated conditions in Experiment 1, the larger distance of dot jump or the varied directions of the dots' motion. The results show that, when the distance of dot jump is large or when the directions of dots' motion are incoherent, higher-order SM arises more frequently. When local first-order motion signals are weakened by appropriate temporal and spatial conditions or by incoherent motion directions, higher-order SM dominates and it captures the motion of dots.     

On the selective effects of a patterned masking stimulus.

Investigated previous findings which suggest that a patterned masking stimulus, presented immediately following tachistoscopic presentation of letter rows, produces large decrements in the recall of letters from the central positions in the rows but has little effect on recall from either end of the displays. 4 experiments with 92 undergraduate Ss confirm the existence of a selective masking effect. The effect was obtained following exposure durations which varied from 30-200 msec. and with both full- and partial-report techniques. Also the selective masking effect was limited to multiletter displays in that it was shown that single letters were masked equally well across the positions used for an entire row. Results suggest that both ends of multiletter displays are processed and identified before the center positions of the displays are processed. (French summary) (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time, distance, and feature trade-offs in visual apparent motion.

A model of visual apparent motion is derived from 4 observations on path selection in ambiguous displays in which apparent motion of illuminated dots could, in principle, be perceived along many possible paths: (a) Whereas motion over each path is clearly visible when its stimulus is presented in isolation, motion is usually seen over only 1 path when 2 or more such stimuli are combined (competition). (b) Path selection is nearly independent of viewing distance (scale invariance). (c) At transition points between paths i and j (where apparent motion is equally likely to be perceived along i and j), the time t and distance d between successive points along the paths are described by a log linear d/t relationship. (d) When successive elements along a path differ in orientation or size, the perceived motion along this path is not necessarily weaker than motion along a path composed entirely of identical elements. The model is a form of strength theory in which the path with greatest strength becomes the dominant path. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic, state-dependent thresholds for the perception of single-element apparent motion: bistability from local cooperativity

Previous studies have indicated that the formation of coherent patterns for multielement motion displays depends on global cooperative interactions among large ensembles of spatially distributed motion detectors. These interactions enhance certain motion directions and suppress others. It is reported here that perceiving one element moving between two nearby locations likewise is subject to cooperative influences (possibly facilitating and inhibiting interactions within a local ensemble of overlapping detectors). Thresholds depending on luminance contrast were measured for a generalized single-element apparent-motion stimulus, and evidence for spontaneous switching and hysteresis effects indicated that motion perception near the 50% threshold was bistable. That is, for conditions in which motion and nonmotion were perceived half the time, the two percepts were distinct; when one was perceived, it clearly was discriminable from the other. These results indicated that (1) single-element apparent-motion thresholds depended on the immediately preceding state of the ensemble of motion detectors responding to the stimulus, and (2) the stimulus activation of individual motion detectors always might be influenced by recurrent, cooperative interactions resulting from the detectors' being embedded within interconnected ensembles.     

The time-order error in judgments of duration.

Three experiments investigated time-order error (TOE) in comparative judgments of duration. 13 Ss were presented sequentially 2 light flashes of either long (900–2,200 msec) or short (70–260 msec) duration and instructed to judge which flash was longer. Overall results show that for both sets of durations, TOE became increasingly negative as the duration in a pair increased and that the errors were more positive for a set of short durations than for a set of long durations. It is argued that these data are compatible with a model for duration judgments which places the source of the error in the decision process. It is suggested that the data described by D. G. Jamieson and W. M. Petrusic (see PA, Vol 54:169; Vol 55:3601) are not inconsistent with this view. (French summary) (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A 13-year follow-up of treatment and snail control in an area endemic for Schistosoma mansoni in Brazil: incidence of infection and reinfection

Transverse relaxation times were estimated from numerical simulations on spin systems using multi-echo spin-echo MRI protocols. The influence of T1 on the echo amplitudes via stimulated echo components was studied. The resulting effects on T2 estimates from the Carr-Purcell (CP), Carr-Purcell-Meiboom-Gill (CPMG), and Phase-Alternating-Phase-Shift (PHAPS; combination of CP and CPMG), multiple echo schemes were examined. Protocols with either spatially selective or nonselective refocusing pulses were studied. An intravoxel static field inhomogeneity of 0.1, 1, and 10 ppm was stimulated. The dependence on T1 of the T2 estimates was notable for T1 values below approximately 800 msec for all protocols. The PHAPS scheme provided rather accurate, but underestimated, T2 values when selective refocusing was used. With nonselective refocusing, PHAPS T2 values were overestimated and demonstrated a pronounced dependence on magnetic field inhomogeneity. In general, long T2 values were erroneous with the PHAPS protocol. The results indicate that a CPMG protocol structure provides a more robust method for T2 estimations than the PHAPS protocol.     

Design of an Arabic near visual acuity chart

This paper describes the design of an Arabic test chart for measurement of visual acuity at near. The chart was designed employing specially selected Arabic letters and was based on the logMAR principle devised by Bailey and Lovie. Ten Arabic letters of nearly equal legibility values (0.92-1.05) (mean = 1.00), (SD = 0.05) were used in the design of the chart. Each row of the chart has 5 letters and row legibility values range from 4.82 to 5.03 with a mean of 4.92 (SD = 0.06). The logMAR method of visual acuity scaling was used, hence the sizes of letters in the rows progress in a uniform step of 0.1 log unit. The inter-letter spacing is equal to the width of each letter in the row, while inter-row spacing is equal to the height of letter in the subjacent row. The height of letters ranged from 3.67 to 0.46 mm corresponding to visual acuity of 2.4 M to 0.3 M which is equivalent to reduced Snellen 6/36 to 6/4.5 at 0.4 m. The chart is designed for use at 40 cm with a recommended luminance level of 160 cd/m2.     

Behavioral measurement of the neural refractory periods for stimulus-bound eating and self-stimulation in the rat.

Subjected 4 albino Sprague-Dawley rats to electrical brain stimulation in pulse pairs. The duration of stimulus-bound eating and rate of self-stimulation were each measured as functions of intrapair interval (IPI). Eating increased sharply when the IPI exceeded .6-.8 msec, and self-stimulation increased when the IPI exceeded .8-1.2 msec. These values are interpreted as the refractory periods of the directly stimulated neurons involved in those behaviors. As the same Ss were used for both experiments and other stimulus parameters were comparable, it is concluded that different sets of neurons are involved in the 2 behaviors. In a 3rd experiment, food deprivation increased the rate of self-stimulation for 1 S, but not for the other 3. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motion detection on flashed, stationary pedestal gratings: evidence for an opponent-motion mechanism

Contrast thresholds were measured for discriminating left vs right motion of a vertical, 1 c/deg luminance grating lasting for one cycle of motion. This test was presented on a 1 c/deg stationary grating (pedestal) of twice-threshold, flashed for the duration of the test motion. Lu and Sperling [(1995). Vision Research, 35, 2697-2722] argue that the visual system detects the underlying, first-order motion of the test and is immune to the presence of the stationary pedestal (and the 'feature wobble' which it induces). On the contrary, we observe that the stationary pedestal has large effects on motion detection at 7 and 15 Hz, and smaller effects at 0.9-3.7 Hz, evidenced by a spatial phase dependency between the stationary pedestal and moving test. At 15 Hz the motion threshold drops as much as five-fold, with the stationary pedestal in the optimal spatial phase (i.e., pedestal and test spatially in phase at middle of motion), and the perceived direction of the test motion reverses with the pedestal in the opposite phase. Phase dependency was also explored using a very brief (approximately 1 msec) static pedestal presented with the moving test. The pedestal of Lu and Sperling (flashed for the duration of the test) has a broad spectrum of left and right moving components which interact with the moving test. The pedestal effects can be explained by the visual system's much higher sensitivity to the difference of the contrast of right vs left moving components than to either component alone.     

Considerations for the Design of Intercepting Drainage for Collecting Water from Seep Areas

Springs that appear at multiple sites on sloping lands and create problems of excess soil moisture and reduced crop yield require the implementation of a network of intercepting drains. The water removed by the intercepting drains also needs to be conducted to a collecting shaft or main drain, whereby it can be safely utilized or discharged back to a lower-lying position in the landscape. In this paper, we present a design method for establishing the position of the first row of interceptor drains and the number of successive rows of intercepting drains, as well as the distances between them. The first row of intercepting drains must be placed upstream of the upper limit of the wet area, through those points at which water-bearing material is found at 40–50?cm underground. The number of rows of necessary intercepting drains is determined from the ratio between the thickness of water-bearing material and the thickness of the filter+drain. For multiple springs that are concentrated on the surface of sloping lands, we propose the solution of a collecting chamber with a side drain and bottom filter.     

Psychophysical Test for the Independence of Perception and Action.

Research has suggested that perception and action are independent (see M. A. Goodale & A. Haffenden, 1998). The authors used the Ebbinghaus illusion to test this hypothesis in 2 experiments. Verbal reports of perceived size were compared with maximum grip aperture during grasping (Experiment 1) and manual reports of perceived size (Experiment 2). A multidimensional signal detection analysis was used to distinguish among the possible interactions between the two processes in each experiment (H. Kadlec & J. T. Townsend, 1992a, 1992b). In Experiment 1, the percepts were independent, and there were no interactions between processes for verbal and visuomotor responses. In Experiment 2, the percepts associated with verbal and manual reports were independent, but the processes interacted at the levels of the stimulus information and the decision rules used to transform each percept into a response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Constraints common to apparent motion in visual, tactile, and auditory space.

A point-like stimulus was presented in a clockwise or counterclockwise sequence at 3, 4, 6, or 12 uniformly spaced locations around a circle in visual, tactile, or auditory space. In 4 experiments, the simulators were (a) light-emitting diodes in the frontal plane, (b) mechanical stimulators on the palm, (c) airpuff nozzles around the head, and (d) loudspeakers around the head. For each spatial separation and stimulus-onset asynchrony (SOA) between successive stimuli around the circle, participants reported the direction of motion. Within each modality, the SOA required for 75% accurate discrimination of direction increased with the spatial separations. A time–distance constraint akin to Korte's third law of visual apparent motion can thus be obtained from responses that are objectively classifiable as correct or incorrect (without relying on subjective reports of "goodness" of apparent motion). Moreover, this time-distance constraint evidently generalizes across sensory modalities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ordinal properties of perceived average duration: Simultaneous and sequential presentations.

When an S evaluates the duration of 2 simultaneous events, the perceived durations are combined in a nonlinear manner, whereas comparable evaluations of successive events yield linear combinations. In the present study, 54 undergraduates rated average durations of pairs of time intervals ranging from 0.5 to 10.0 sec. The intervals making up a pair were presented successively and simultaneously on separate occasions within the same presentation sequence. The order of data was consistent with models previously proposed for perceived average duration. A nonmetric analysis of the combined ordinal data from both conditions yielded a single set of measures of perceived duration with ratio-scale properties. The common scale for the 2 conditions is consistent with differences in results from simultaneous and successive monitoring of time intervals, stemming from differences in the way duration information is combined rather than how it is perceived. The derived scale is related to physical time by a power function with a 1.06 exponent. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial effects on tactile duration categorization.

The aim of this study was to measure the impact of the distance between tactile stimuli marking brief time intervals on perceived duration and threshold estimates. Each interval to be categorized as short or long (midvalue = 500 ms) was marked by two brief signals delivered on participants' left (L) or right (R) hand: L-L, R-R, L-R or R-L. The hands were placed nearby or at a distance of 3 feet (about 91 cm). Eight-point individual psychometric functions were drawn for each of the eight experimental conditions. The results reveal that when intervals are marked with signals delivered on different hands rather than on the same hand, they are perceived as longer. Moreover, no difference for perceived duration was observed between the L-L and R-R conditions, and between the L-R and R-L sequence. Finally, marking intervals with signals delivered at the same hand results in better temporal discrimination than with one signal delivered on each hand. The results with perceived duration are consistent with the kappa effect, but not with an attentional account of duration discrimination. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Auditory habituation in young and older adults: The verbal transformation effect.

In 3 experiments, auditory massed repetition was used to examine age-related differences in habituation by means of the verbal transformation paradigm. Participants heard 10 words (5 high frequency and 5 low frequency), each presented 180 times, and they reported perceived changes in the repeated words (verbal transformations). In these experiments, older adults reported fewer illusory percepts than young adults. Older adults' loss of auditory acuity and slowing of processing, stimulus degradation (in young adults), and instructions biasing the report of these illusory percepts did not account for the fewer illusory percepts reported by the older adults. These findings suggest that older adults' reduced susceptibility to habituation arises from centrally located declines in the transmission of information within the word recognition pathway. The discussion focuses on the implications that these age-related declines may have on word identification during on-line speech perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Novel popout: Empirical boundaries and tentative theory.

Observers received glimpses of 4-word arrays and were probed for the locations of particular words. Familiar words were repeated across arrays but novel words were not. Accuracy was higher for familiar than for novel arrays, but this baseline difference was diminished when a single novel word appeared with 3 familiar words. In these arrays, accuracy rose above baseline for novel words, defining novel popout (NPO), and fell below baseline for familiar words, defining familiar sink-in (FSI). In Exps 1–4, NPO remained intact and FSI actually increased as duration of array exposure was reduced from 200 msec to as brief as 33 msec. At brief exposures, even familiar words popped out from fields in which they had never before appeared. NPO is attributed to the distribution of locations associated with bottom-up-top-down mismatches. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-stimulation in the rat: Quantitative characteristics of the reward pathway.

Quantitative characteristics of the neural pathway that carries the reinforcing signal in electrical self-stimulation of the male Sprague-Dawley rat's brain were established by finding which combinations of stimulation parameters give the same performance in a runway. The reward for each run was a train of evenly spaced monophasic cathodal pulses from a monopolar electrode. With train duration and pulse frequency held constant, the required current was a hyperbolic function of pulse duration, with chronaxie c?=?1.5 msec. With pulse duration held constant, the required strength of the train (the charge delivered per second) was a hyperbolic function of train duration, with chronaxie C?=?500 msec. To a first approximation, the values of c and C were independent of the choice either of train duration and pulse frequency or of pulse duration, respectively. Hence, the current intensity required by any choice of train duration, pulse frequency, and pulse duration depended on only 2 basic parameters, c and C, and 1 quantity, Qi, the required impulse charge. These may reflect, respectively, current integration by directly excited neurons; temporal integration of neural activity by synaptic processes in a neural network; and the peak of the impulse response of the network, assuming that the network has linear dynamics and that the reward depends on the peak of the output of the network. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)