Gray Chips Research Articles

The resonant dynamics of speech perception: interword integration and duration-dependent backward effects.

How do listeners integrate temporally distributed phonemic information into coherent representations of syllables and words? For example, increasing the silence interval between the words "gray chip" may result in the percept "great chip," whereas increasing the duration of fricative noise in "chip" may alter the percept to "great ship" (B. H. Repp, A. M. Liberman, T. Eccardt, & D. Pesetsky, 1978). The ARTWORD neural model quantitatively simulates such context-sensitive speech data. In ARTWORD, sequentially stored phonemic items in working memory provide bottom-up input to unitized list chunks that group together sequences of items of variable length. The list chunks compete with each other. The winning groupings feed back to establish a resonance which temporarily boosts the activation levels of selected items and chunks, thereby creating an emergent conscious percept whose properties match such data.

Lightness contrast and failures of constancy: a common explanation.

Observers were asked to select, from a grid of 16 achromatic Munsell chips presented on a white background in bright illumination, a sample to match a light gray chip simultaneously presented on the same white background but in a shadowed region adjacent to the brightly illuminated region. The border dividing the two fields of illumination was made to appear as either a reflectance edge or an illumination edge by either concealing or revealing the larger context. Each condition thus constituted an experiment on either contrast or constancy, allowing these two phenomena to be compared under comparable conditions. The results indicate that constancy effects are far greater than contrast effects, casting doubt on conventional reductions of the two phenomena to a single explanatory mechanism. Closer analysis of the data indicates that it may be contrast effects andfailures of constancy that share a common explanation. Such an explanation, in terms of edge-processing algorithms, is offered and is supported with additional experiments as well as a brief review of previous contrast and constancy findings.

Perceptual integration of acoustic cues for stop, fricative, and affricate manner.

Introducing a short interval of silence between the words SAY and SHOP causes listeners to hear SAY CHOP. Another cue for the fricative-affricate distinction is the duration of the fricative noise in SHOP (CHOP). Now, varying both these temporal cues orthogonally in a sentence context, we find that, within limits, they are perceived in relation to each other: The shorter the duration of the noise, the shorter the silence necessary to convert the fricative into an affricate. On the other hand, when the rate of articulation of the sentence frame is increased while holding noise duration constant, a longer silent interval is needed to hear an affricate, as if the noise duration, but not the silence duration, were effectively longer in the faster sentence. In a second experiment, varying noise and silence durations in GRAY SHIP, we find that given sufficient silence, listeners report GRAY CHIP when the noise is short but GREAT SHIP when it is long. Thus, the long noise in the second syllable disposes listeners to displace the stop to the first syllable, so that they hear not a syllable-initial affricate (i.e., stop-initiated fricative) but a syllable-final stop (followed by a syllable-initial fricative). Repeating the experiment with GREAT SHIP as the original utterance, we obtain the same pattern of results, together with only a moderate increase in GREAT responses. In all such cases, the listeners integrate a numerous, diverse, and temporally distributed set of acoustic cues into a unitary phonetic percept. These several cues have in common only that they are the products of a unitary articulatory act. In effect, then, it is the articulatory act that is perceived.

Some relations between duration of silence and duration of friction noise as joint cues for fricatives, affricates, and stops

As is well known, introducing a short interval of silence between the words SAY and SHOP causes the listener to hear SAY CHOP. In isolation, SHOP may be turned into CHOP by reducing the duration of the friction noise. Now, varying both cues orthogonally in a sentence context, we find that, within limits, they are perceived in relation to each other: The shorter the duration of the noise, the shorter the silence necessary to convert the fricatives into an affricate. On the other hand, when the rate of articulation of the sentence frame is increased while holding noise duration constant, a longer silent interval is needed to hear an affricate, as if the noise duration, but not the silence duration, were subjectively longer in the faster sentence. In a separate experiment, varying noise and silence durations in GRAY SHIP, we find that, given sufficent silence, listeners report GRAY CHIP when the noise is short, but GREAT SHIP when it is long. Thus, the long noise in the second syllable disposes the listeners to displace the stop to the first syllable, so that they hear not a syllable-initial affricate (i.e., stop-initiated fricative) but a syllable-final stop (followed by a syllable-initial fricative). [Work supported by NICHD.]

Brightness discrimination in reflected laser light

Brightness discrimination judgments for gray chips were made by 12 male human Ss using the psychophysical method of limits. White, noncoherent red, and He-Ne laser light sources of equal power were used. The data showed poorer discrimination from white to red to laser light and better discrimination when trials started from the darker end of the stimulus range. Results are discussed in terms of human spectral sensitivity, masking effect of the standing diffraction pattern in laser light, and brightness contrast between the stimulus and surround.

Does context influence the shape of a perceptual scale?

Effects of backgroun reflectance on the shapes of scales of lightness were investigated in two experiments. In Experiment I, 25 Ss compared similaritiesofpairs ofgray chips that were viewed against black, gray. or white backgrounds. In Experiment 2, 33 Ss positioned a series of gray chips, viewed against a white, gray. or black background, so that the distances between successive chips represented the perceived differences in lightness between them. The results of both studies indicated that scale shape was influenced by background. The nature of the effect was that interstimulus differences in the region of a background were enhanced relative to interstimulus differences far from a background.