Spatial and fixation conditions affecting the temporal course of changes in perceived relative distance

The results of two experiments are reported in which the change over time in the perceived depth location of a monocular, luminous test object with respect to two binocular luminous stimuli located at different distances was measured. It was found that: 1) The test object receded perceptually in depth over time achieving a stable location in space after 4 min of viewing. 2) The initial perceived location in depth of the test object depended upon which of the two binocular objects was fixated. When the farther binocular object was fixated the test object appeared further away than when the nearer one was fixated. 3) The size of the further binocular object also affected the initial perceived location of the test object. When it was larger, the test object appeared further away than when it was smaller. 4) There was an interaction between the binocular object fixated upon and the lateral separation between it and the test object: the smaller the separation, the greater the fixation effect.These results were accounted for in terms of the equidistance tendency, the depth adjacency principle, and a possible attentional factor. Taken together the results indicate that while reduced viewing conditions reduce the available stimulus information, they do not reduce the organizational options of the visual system.     

Induced loudness reduction as a function of frequency difference between test tone and inducer

When a high-intensity tone (inducer) is followed by a moderate-intensity tone (test tone), the loudness of the latter is reduced. This phenomenon, called induced loudness reduction (ILR), depends on the frequency separation of the two tones; as the difference in frequency increases, the amount of ILR decreases. However, the precise course of this decrease is not well known. This article presents two experiments that address this question. In the first experiment, the amount of loudness reduction produced by a 2.5-kHz 80-dB-SPL inducer was measured with the frequency of the test tone swept from 800 Hz to 6 kHz. In the second experiment, the amount of ILR was measured with the same inducer and with test tones set at 2, 2.5, 3, and 4 kHz. Both experiments show that some ILR occurs at frequency separations as wide as four critical bands.     

Auditory induction: Reciprocal changes in alternating sounds

When portions of a sound are replaced by a potential masker, the missing fragments may be perceptually restored, resulting in apparent continuity of the interrupted signal. This phenomenon has been examined extensively by using pulsation threshold, auditory induction, and phonemic restoration paradigms in which two sounds, the inducer and the inducee, are alternated (ABABA ... ), and the conditions required for apparent continuity of the lower amplitude inducee are determined. Previous studies have generally neglected to examine concomitant changes produced in the inducing sound. Results from the present experiments have demonstrated decreases in the loudness of inducers using inducer/inducee pairs consisting of tone/tone and noise/noise, as well as the noise/speech pairs associated with phonemic restorations. Interestingly, reductions in inducer loudness occurred even when the inducee was heard as discontinuous, and these decreases in loudness were accompanied by graded increases in apparent duration of the inducee, contrary to the conventional view of auditory induction as an all-or-none phenomenon. Under some conditions, the reduced loudness of the inducer was coupled with a marked alteration in its timbre. Especially profound changes in the inducer quality occurred when the alternating stimuli were tones having the same frequency and differing only in intensity-it seems that following subtraction of components corresponding to the inducee, an anomalous auditory residue remained that did not correspond to the representation of a tone.     

Effects of the build-up and resetting of auditory stream segregation on temporal discrimination

The tendency to hear a tone sequence as 2 or more streams (segregated) builds up, but a sudden change in properties can reset the percept to 1 stream (integrated). This effect has not hitherto been explored using an objective measure of streaming. Stimuli comprised a 2.0-s fixed-frequency inducer followed by a 0.6-s test sequence of alternating pure tones (3 low [L]-high [H] cycles). Listeners compared intervals for which the test sequence was either isochronous or the H tones were slightly delayed. Resetting of segregation should make identifying the anisochronous interval easier. The HL frequency separation was varied (0-12 semitones), and properties of the inducer and test sequence were set to the same or different values. Inducer properties manipulated were frequency, number of onsets (several short bursts vs. one continuous tone), tone:silence ratio (short vs. extended bursts), level, and lateralization. All differences between the inducer and the L tones reduced temporal discrimination thresholds toward those for the no-inducer case, including properties shown previously not to affect segregation greatly. Overall, it is concluded that abrupt changes in a sequence cause resetting and improve subsequent temporal discrimination.     

Auditory pattern perception: the effect of tone location on the discrimination of tonal sequences.

This study examined the effect of tonal location on the discrimination of sequences differing in the order of the tones and on their perceived grouping. The frequency range between the sequential tones was held constant. When all tones came from the same location, the sequence was rated as integrated, but when the higher frequency tones came from a different location than the lower frequency tones, the sequence was rated as segregated. Listeners discriminated the sequences in a 3IFC task. Discrimination performance was impaired when the sequence was split between two locations and tonal order was changed in only one location, even though the order of tones in different locations was changed. This result suggests that listeners have difficulty relating tones across locations or in different perceptual groups. Performance in this experiment is generally better than that observed by Barsz (1988), and it is suggested that the level of stimulus uncertainty explains this difference.     

Auditory pattern perception: The effect of tone location on the discrimination of tonal sequences

This study examined the effect of tonal location on the discrimination of sequences differing in the order of the tones and on their perceived grouping. The frequency range between the sequential tones was held constant. When all tones came from the same location, the sequence was rated as integrated, but when the higher frequency tones came from a different location than the lower frequency tones, the sequence was rated as segregated. Listeners discriminated the sequences in a 3EFC task. Discrimination performance was impaired when the sequence was split between two locations and tonal order was changed in only one location, even though the order of tones in different locations was changed. This result suggests that listeners have difficulty relating tones across locations or in different perceptual groups. Performance in this experiment is generally better than that observed by Barsz (1988), and it is suggested that the level of stimulus uncertainty explains this difference.     

Posttransient shifts in auditory lateralization

Presenting an intense (e.g., 80-dB [SPL]) "transient" (e.g., 50-msec) inducer to the ear reduces the loudness of subsequent signals at or near the frequency of the inducer. In this study, we ask whether similar inducers also affect lateralization. In two experiments, we asked how inducing tones presented to one ear (the exposed ear) affect judgments of the lateral position of subsequent target tones having various interaural intensity differences. In Experiment 1, inducers had the same frequency as the targets, and, as predicted, reduced the tendency to lateralize the targets to the exposed ear. In Experiment 2, the frequency of the inducers and the target differed (different critical bands), thereby eliminating the effect on lateralization. These results are consistent with the hypothesis that inducers temporarily reduce the magnitude of the representation of intensity signals in the frequency region around them and that this reduction occurs, at least partly, peripherally to the site at which binaural intensity differences are encoded. The results imply further that the reduction in loudness previously reported under similar stimulus conditions reflects a more general reduction of intensity-based information in hearing.     

A linear relation between loudness and decibels

A total of 37 uninitiated observers made repeated numerical magnitude judgments of the loudness of a sequence of octave band noises spaced at 1-dB intervals, from 0 to 5 dB above a standard of about 80 dB(A), which was called 10. The observers were not instructed to use numbers as ratios. When the median responses are plotted linearly against decibels, they are fitted by straight lines. Each extra decibel adds an average of 1 unit of loudness, range for individual observers 10 through .25 units. This is consistent with the view that the subjectively equal stimulus spacing for the loudness of noise is linear in decibels, and that the observers use numbers linearly in judging the loudness.     

Are correlated streams of information necessary for implicit sequence learning?

We investigated whether the existence of correlated streams of information is necessary for incidental sequence learning to occur. We ran three separate experiments with a total of 201 undergraduate students. Each experiment had at least one condition with two streams of sequenced information that were correlated. The correlations differed in terms of the kind of responses that were required, the kind of tasks and stimuli, the on-screen locations at which they occurred and how they were combined. Only in conditions with correlated sequences was implicit sequence learning found. Our results suggest that the presence of correlated streams of information may be the main pre-requisite for implicit sequence learning.     

Distributed planning of movement sequences

Three experiments are reported that examine whether fast finger-tapping sequences are entirely planned before execution starts (advance planning), or if they can be started while planning is still under way (distributed planning). Subjects performed finger tapping sequences of three to eight taps at a high rate, under both simple and 2-choice reaction time (RT) conditions. The sequences differed in the location of an accentuated element within them. The RT to choose between sequences with different accent locations progressively decreased as an inverse function of the time-distance between the initial tap and the first point at which the alternative sequences differed. The shortening in choice reaction time (CRT) was never accompanied by noticeable changes in the inter-response times or force patterns of the tapping sequences. The RT to initiate sequences with accent location known beforehand (SRT condition) showed, in two of three experiments, a weak decreasing trend as the accentuated tap shifted away from the beginning of the sequence. The SRT results suggest a possible predominance of advance planning when the same sequence is repeated over a series of trials. The CRT results are taken as evidence that planning of the sequence beyond the unpredictable tap could be distributed before and after sequence initiation. Several factors are discussed that may influence the balance between planning in advance of, and planning in parallel with, sequence execution.     

Distributed Planning of Movement Sequences

Three experiments are reported that examine whether fast finger-tapping sequences are entirely planned before execution starts (advance planning), or if they can be started while planning is still under way (distributed planning). Subjects performed finger tapping sequences of three to eight taps at a high rate, under both simple and 2-choice reaction time (RT) conditions. The sequences differed in the location of an accentuated element within them. The RT to choose between sequences with different accent locations progressively decreased as an inverse function of the time-distance between the initial tap and the first point at which the alternative sequences differed. The shortening in choice reaction time (CRT) was never accompanied by noticeable changes in the inter-response times or force patterns of the tapping sequences. The RT to initiate sequences with accent location known beforehand (SRT condition) showed, in two of three experiments, a weak decreasing trend as the accentuated tap shifted away from the beginning of the sequence. The SRT results suggest a possible predominance of advance planning when the same sequence is repeated over a series of trials. The CRT results are taken as evidence that planning of the sequence beyond the unpredictable tap could be distributed before and after sequence initiation. Several factors are discussed that may influence the balance between planning in advance of, and planning in parallel with, sequence execution.     

Binaural release from temporal induction

This study examined the effects of interaural phase difference (IPhD) relations in temporal induction (TI)—that is, the perceived continuity of a fainter sound (inducee) through an interrupting higher amplitude sound (inducer). The extent of TI was measured both directly as the upper amplitude level for continuity and indirectly as the loudness reduction of the inducer. It was found that TI was inhibited when the IPhD of the inducer and the IPhD of the inducee differed. It was also found that the extent of induction was positively related to the masking potential of the inducer as measured by the binaural masking level difference procedure. These results suggest that TI involves processes that are affected by interaural phase differences and that the masking potential rule, shown by previous studies to apply in the frequency domain, applies also in the IPhD domain. The present findings are consistent with the hypothesis that TI results from allocation of a portion of the neural excitation produced by the inducer over to the inducee if the inducer has the appropriate masking potential. As a consequence, obliterated signals can be selectively restored on the basis of both frequency-specific monaural cues and azimuth-related binaural cues, abilities that can enhance detection of signals under the noisy conditions of everyday life.     

Attentional limitations in processing sequentially presented vibrotactile targets

In seven experiments, participants experienced rapid, serially presented streams of vibrations and responded to specific targets in the streams. In visual (and sometimes auditory) streams presented in this manner, it is typical to find a deficit in reporting the second of two targets when both must be reported and the second appears within a short temporal interval of the first, but not when identical displays are presented but only the second target must be reported (e.g., the attentional blink, or AB). This conventional AB pattern was found in the last experiment, in which judgments were about target location. However in the first six experiments reported here, in which judgments were about frequency, intensity, duration, or location of targets, accuracy was dependent on target separation regardless of whether or not the first target was reported. This unconventional pattern could represent an AB if the first target was attended even when it was not reported. The evidence for this claim and an alternative possibility that location judgments are especially sensitive to attention manipulations are discussed.     

Does stimulus context affect loudness or only loudness judgments?

Marks (1988) reported that when equal-loudness matches were inferred from magnitude estimates of loudness for tones of two different frequencies, the matches were affected by changes in the stimulus intensity range at both frequencies. Marks interpreted these results as reflecting the operation of response biases in the subjects' estimates; that is, the effect of range was to alter subjects' judgments but not necessarily the perception of loudness itself. We investigated this effect by having subjects choose which of two tone pairs defined the larger loudness interval. By using tones of two frequencies, and varying their respective intensity ranges, we reproduced Marks' result in a procedure devoid of numerical responses. When the tones at one frequency are all soft, but the tones at the other frequency are not all soft, cross-frequency loudness matches are different from those obtained with other intensity range combinations. This suggests that stimulus range affects the perception of loudness in addition to whatever effects it may have on numerical judgments of loudness.     

The control of food-caching behavior by Western scrub-jays (Aphelocoma californica)

Western scrub-jays (Aphelocoma californica) did not show extinction when caching behavior was never rewarded and they had no choice of where to cache the food. However, when the jays had the choice of caching items in 2 different locations or during 2 successive episodes, and only 1 of each was always rewarded at recovery, they rapidly learned to cache in the rewarded location or episode. When the jays had learned during training trials that their caches were always moved to 1 of 2 locations they did not cache in, then on the test trial they cached in the location that had been previously rewarded. To test whether these jays avoided the location in which their caches had been pilfered or chose the rewarded location, the procedure was repeated to include a 3rd location that was never rewarded. The jays avoided the pilfered location but cached equally in the rewarded and nonrewarded locations.     

Individual loudness functions determined from direct comparisons of loudness intervals

Five subjects were required in each trial to directly compare two pairs of tones and indicate which pair of tones had the greater loudness difference. Ten 1,200-Hz tones differing only in intensity were employed. Subjects made binary comparisons among the 45 tone pairs that can be formed from these 10 tones. The loudness difference comparisons of each subject were found to satisfy two properties (transitivity and monotonicity) that are required for an interval scale representation of loudness. Therefore, individual loudness scales were constructed using a nonmetric scaling technique designed for comparisons of sensory intervals. These loudness scales differed significantly from subject to subject. Since a nonnumerical scaling procedure was employed, these individual differences could not be attributed to biases in the way in which observers use numbers or numerical concepts to describe the loudness of tones. Hence, they suggest strong individual differences in the coding of sound intensity.     

The influence of melodic context on pitch recognition judgment

Subjects made delayed pitch comparisons between tones that were each preceded by tones of lower pitch. The pitches of these preceding tones were so chosen that in some conditions the melodic intervals formed by the standard (S) and comparison (C) combinations were identical, and in others they differed. A strong effect of melodic relational context was demonstrated. When the S and C combinations formed identical melodic intervals, there was an increased tendency for the S and C tones to be judged as identical. And when the S and C combinations formed different melodic intervals, there was an increased tendency for the S and C tones to be judged as different. These effects occurred both when the S and C tones were identical in pitch and also when these differed, and they occurred despite instructions to attend only to the S and C tones.     

Statistical computations over a speech stream in a rodent

Statistical learning is one of the key mechanisms available to human infants and adults when they face the problems of segmenting a speech stream (Saffran, Aslin, & Newport, 1996) and extracting long-distance regularities (G6mez, 2002; Pe?a, Bonatti, Nespor, & Mehler, 2002). In the present study, we explore statistical learning abilities in rats in the context of speech segmentation experiments. In a series of five experiments, we address whether rats can compute the necessary statistics to be able to segment synthesized speech streams and detect regularities associated with grammatical structures. Our results demonstrate that rats can segment the streams using the frequency of co-occurrence (not transitional probabilities, as human infants do) among items, showing that some basic statistical learning mechanism generalizes over nonprimate species. Nevertheless, rats did not differentiate among test items when the stream was organized over more complex regularities that involved nonadjacent elements and abstract grammar-like rules.     

Detection and discrimination of coherent motion

When viewing a pair of bars defined by the difference of spatial Gaussian functions (DOGs), human observers can discriminate accurately the relative movements of the bars, even when they differ in spatial frequency. On each trial, observers viewed two brief presentation intervals in which a pair of vertically oriented DOGs moved randomly back and forth within a restricted range. During one interval, both bars moved in the same horizontal direction and by the same magnitude (correlated movements); in the other interval, their movements were uncorrelated. When discrimination accuracy is related to the simultaneous detection of two independent movements, it was found that, if observers can detect the movements of spatially separated bars, they can tell whether their relative movements are correlated. Performance remained remarkably accurate even when the two bars differed in spatial frequency by more than two octaves or were presented separately to the two eyes. Apparently, the accurate discrimination of coherent motion involves an efficient spatial integration of optical motion information over multiple spatial locations and multiple spatial scales.     

Perceptual attenuation of nonfocused auditory streams

The aim of this study was to measure the perceptual attenuation, measured in decibels, resulting from the focusing of attention on one stream within a multistream auditory sequence. The intensity of a nonfocused stream was increased until the accuracy of detecting a temporal irregularity in this stream was the same as in a focused stream. Eight subjects were required to detect a temporal irregularity created by delaying or advancing one tone which could be situated in one of three temporally regular streams played simultaneously to create a multistream sequence. The three streams differed in tempo and frequency. Subjects’ attention was focused on one of the streams by preceding the multistream sequence with one of the single streams (a cue). We first established the size of temporal irregularity detected at a 90% level in cued streams, confirming that subjects were able to focus on one particular stream. Second, an irregularity of this size was not detected above chance level in noncued streams, demonstrating that listeners focus only on the cued stream. Third, for 5 subjects, a 15-dB increase in the level of one of the noncued streams was necessary to bring detection up to that found in the cued streams. This gain provides an equivalent measure of the perceptual attenuation of nonfocused streams. For 3 other subjects, detection in the noncued stream remained at chance performance whatever the level. For all subjects, detection in the cued stream decreased slightly as the level of the noncued stream increased. We conclude that the attenuation of nonfocused auditory streams can attain as much as 15 dB, at least for some subjects.