Donna Kat

Inhibition of return: A graphical meta-analysis of its time course and an empirical test of its temporal and spatial properties

Immediately after a stimulus appears in the visual field, there is often a short period of facilitated processing of stimuli at or near this location. This period is followed by one in which processing is impaired, rather than facilitated. This impairment has been termed inhibition of return (IOR). In the present study, the time course of this phenomenon was examined in two ways. (1) A graphical metaanalysis plotted the size of the effect as a function of the stimulus onset asynchrony (SOA) of the two stimuli. This analysis showed that IOR is impressively stable for SOAs of 300-1,600 msec. It also showed that the literature does not provide any clear sense of the duration of IOR. (2) An empirical approach was, therefore, taken to fill this gap in our knowledge of IOR. In three experiments, IOR was tested using SOAs between 600 and 4,200 msec. IOR was robust for approximately 3 sec and appeared to taper off after this point; the observed duration varied somewhat as a function of the testing conditions. In addition, for the first second, the degree of inhibition was inversely related to distance of the target from the original stimulus, but for the next 2 sec this spatial distribution was not observed. Theories of the mechanisms and function of IOR must conform to these spatial and temporal properties.

Perception of intervocalic stop consonants: The contributions of closure duration and formant transitions

Acoustic analyses of vowel-consonant-vowel (VCV) utterances indicate that they generally include formant transitions from the first vowel into a period of closure (VC transitions), and transitions out of the closure into the second vowel (CV transitions). Three experiments investigated the perceptual importance of the VC transitions, the CV transitions, and the closure period in identification of medial stop consonants varying in place of articulation. Experiment 1 compared identification of members of synthetic VC and CV continua with those from VCV series made by concatenating corresponding VC and CV stimuli using various closure durations. Experiment 2 examined identification of VCV stimuli constructed with only VC, only CV, or both VC and CV transitions; again closure duration was systematically varied. Experiment 3 correlated CV and VC identification with identification of VCV stimuli. Neither closure duration nor formant transition structure (i.e., only VC, only CV, or both) had an independent effect on identification. Instead, the formant structure and closure duration together strongly affected stop identification. When both VC and CV transitions were present, the CV transitions contributed somewhat more to identification of medial stops with short closures, than the VC transitions did. With longer closure durations, neither set of transitions appeared to determine perceived place of articulation in any simple way. Overall, the data indicate that the perception of a medial consonant is more than simply a (weighted) sum of its parts.

Adaptation is automatic

Two experiments were used to test whether selective adaptation for speech occurs automatically or instead requires attentional resources. A control condition demonstrated the usual large identification shifts caused by repeatedly presenting an adapting sound (/wa/, with listeners identifying members of a /ba/-/wa/ test series). Two types of distractor tasks were used: (1) Subjects did a rapid series of arithmetic problems during the adaptation periods (Experiments 1 and 2), or (2) they made a series of rhyming judgments, requiring phonetic coding (Experiment 2). A control experiment (Experiment 3) demonstrated that these tasks normally impose a heavy attentional cost on phonetic processing. Despite this, for both experimental conditions, the observed adaptation effect was just as large as in the control condition. This result indicates that adaptation is automatic, operating at an early, preattentive level. The implications of these results for current models of speech perception are discussed.

Which syllable does an intervocalic stop belong to? A selective adaptation study

Three selective adaptation experiments were conducted to investigate whether intervocalic stops are perceived as the end of the preceding syllable or as the beginning of the following one. The pattern of adaptation effects (and just as importantly, noneffects) indicated that intervocalic stop consonants are perceptually more like syllable-initial than syllable-final ones. From this it might be concluded that the perceptual system breaks down a vowel-consonant-vowel (VCV) utterance into a V-CV sequence. However, the similarity of an intervocalic stop to a syllable-initial one is quite limited; the consonant in a VCV is apparently treated as essentially different from consonants in either VC or CV utterances. These results clarify, and perhaps complicate, the role of the syllable in models of the speech perception process.

More adaptation of speech and nonspeech

In a previous study [A. G. Samuel and E. L. Newport, J. Exp. Psychol.: Hum. Perc. Perf. 5(3), 563–578 (1979)], nonspeech adaptors (440 Hz sawtooth waves and white noise segments, with 0‐ or 80‐ms rise times) caused significant labeling shifts on speech continua. In particular, the abruptly onsetting sawtooth reduced the number of [ba]s reported (versus [wa]), and the gradually onsetting noise segment reduced responses of [sha] (versus [cha]. These results suggested that (1) speech and nonspeech are processed by the same mechanisms, and (2) these mechanisms are sensitive to the general spectral quality of the input, i.e. whether the spectrum is generally flat (aperiodic) or peaked (periodic). In the present study, the same four adaptors were used on a [dɜɑ]—[ɜɑ] continuum. These stimuli have spectra quite similar to [+∫ɑ]—[∫ɑ], but are voiced, and thus have a low‐frequency periodic component. As with [cha]—[sha], only the gradually onsetting noise adaptor was effective. These results indicate that as sugg...

Are selective adaptation effects independent of cognitive load

Selective adaptation occurs through the repeated presentation of a sound (the ‘‘adaptor’’), and leads to a reduction in the perception of similar sounds. Adaptation has been used to investigate the nature of early speech representations. Work in this laboratory has recently demonstrated that perceptually restored phonemes can produce reliable adaptation effects, and that these effects are occurring at relatively early levels (e.g., phonemic rather than lexical) of processing [A. G. Samuel, CognitivePsychology (in press)]. The current study is designed to determine whether the adaptation effects are so low‐level and automatic that they do not require cognitive resources. There are three conditions in the current study: (1) adaptation alone (control), (2) adaptation during continuous arithmetic problems, and (3) adaptation during continuous rhyming judgments (presented visually). Preliminary results indicate that continuously solving arithmetic problems does not reduce the adaptation effect, indicating no g...

Reaction time and dichotic evidence for central processing of complex auditory signals

Extensive work has been done to clarify the number of stages and the mechanisms involved in the recognition of speech. This selective adaptation study examines the effect that individual second and third formants have. compared to the combined effect of both formants; the combination is tested both monaurally and dichotically. Experiment 1 compares the added effects of the individual second and third formants to the effect of an adaptor with combined second and third formants. Experiment 2 examines the effect of variations in amplitude of the adapting formants. The third experiment examines dichotic presentation of the second formant in one ear and the third formant in the other versus binaural presentation of the combined second and third formants. Reaction time results and the labeling shifts suggest a post‐peripheral and integrative mechanism for complex signal processing. [Work supported by AFOSR.]

Using reaction times to explore the mechanisms of selective adaptation

Previous research has demonstrated that the identification shifts induced by selective adaptation are accompanied by reliable reaction time changes. For example, if a /ba/‐/da/ test series is used, reaction times to tokens at the /b/ end of the series will be higher after /ba/ adaptation than after/da/adaptation; at the /da/ end, the reverse is true [A. G. Samuel, Cog. Psychol. 18, 452–499 (1986)]. The present study extends these results in three ways. First, a neutral adaptation condition (/a/) is used to provide an appropriate baseline for measuring absolute reaction time changes. Second, combination adaptors (/ba/‐/da/) are used to look for reaction time changes in the absence of labeling shifts. Third, cross‐series reaction time changes (/pa/,/ta/, and /pa/‐/ta/ on a /ba/‐/da/ series) are examined. The pattern of reaction time changes will be used to address the level of processing affected by adaptation, and to clarify the mechanism of the effects (contrast versus fatigue).

To /b/ or not to /b/: The interaction of intervocalic silence and consonantal transitions

The acoustic realization of a consonant depends upon its position in the syllable. For example in /bɑ/, there are rising transitions; in /ɑb/, there are falling transitions, and in/ɑbɑ/there may be either (/ɑb_ɑ/ or /ɑ_bɑ/), or both (/ɑbba/). The present study investigated the possible interaction of formant transitions (incoming, outgoing, both) and stop‐gap duration in the perception of place of articulation in inter‐vocalic position. Subjects identified tokens from 14 synthetic speech continua: /bɑ/—/dɑ/, its mirror image /ɑb/—/ɑd/, and 12 VCV continua. The VCV continua were constructed by preceding /bɑ/—/dɑ/ with /ɑ/ (/ɑ_bɑ/—/ɑ_dɑ/), following /ɑb/—/ɑd/ with /ɑ/ (/ɑb_ɑ/—/ɑd_ɑ/), and concatenating /ɑb/—/ɑd/ and /bɑ/—dd/ (/ɑbbɑ/— /ɑddɑ/); four silent intervals (0, 25, 50, and 100 msc) were used for each type of VCV series. Subjects labeled more tokens as /b/ in /ɑb/— /ɑd/ than in /bɑ/ɑ/dɑ/. Adding an /a/ to /ɑb/—/ɑd/ decreased /b/ reports, whereas adding it to /bɑ/—/dɑ/ increased such reports; these effects were very large with the 0‐ms stop‐gap, and decreased as gap duration increased. Labeling of the /ɑbbɑ/—/ɑddɑ/ continua was more similar to the /bɑ/—/dɑ/ derived series than the /ɑb/—/ɑd/ series.

Reflections on and of the syllable: Does a medial consonant in a VCV belong to the first or second syllable?

Previous research has shown that adaptation effects in speech are position specific: consonant‐vowel (CV) syllables do not affect labeling of vowel‐consonant (VC} syllables, and vice versa. The present study uses this fact to test whether a medial stop consonant in a VCV utterance belongs to the first syllable, the second syllable, or both. Three test series were constructed: one in which the medial consonant was represented by transitions into the stop (/ɑb_ɑ/—/ɑd_ɑ/), one in which the transitions were out of the stop (/ɑ_bɑ/—/ɑ_dɑ/), and one with both incoming and outgoing transitions (ɑbbɑ/—/ɑddɑ/). Adaptation with /bɑ/, /ɑb/, /ɑ_bɑ/, /ɑb_ɑ/, and /ɑbbɑ/ was conducted on all three continua. The pattern of results is used to address the syllabification issue, and the acoustic‐phonetic issue which has been discussed in the adaptation literature.