Response organization in selective adaptation to speech sounds

Previous experiments in speech perception using the selective adaptation procedure have found a shift in the locus of the category boundary for a series of speech stimuli following repeated exposure to an adapting syllable. The locus of the boundary moves toward the category of the adapting syllable. Most investigators have interpreted these findings in terms of feature detector models in which specific detectors are reduced in sensitivity through repeated adaptation. The present experiment was conducted to determine whether the adaptation results might be due to changes in response organization as a consequence of the labeling instructions presented to subjects in selective adaptation experiments. A perceptually ambiguous speech stimulus was selected from the middle of a [bi]-[di] test series and used as an adaptor under two different sets of instructions. One group of subjects was told that the adapting stimulus was the syllable [bi], while another group was told that the stimulus was the syllable [di]. The acoustically ambiguous adaptor failed to produce a shift in the locus of the category boundary in the direction predicted on the basis of the labeling instructions presented to subjects. These results indicate that the acoustic attributes and perceived quality of the adapting stimulus determine the direction and magnitude of the adaptation effects rather than the labels provided by the experimenter.     

Selective adaptation effects on end-point stimuli in a speech series

Recent experiments in speech perception using the selective adaptation paradigm have found that the phonetic boundary of a test series shifts following adaptation. However, no changes within the phonetic category have been found. In the present experiment, a series of voiced CV syllables which varied along the feature of place was used in a selective adaptation paradigm. The end-point stimuli trom the test series were used as adaptors. Subjects used a 6-point rating scale to respond to the stimuli instead of the usual two-category identification. The average rating for end-point stimuli from the same category as the adaptor, as well as the boundary stimuli, shifted as a function of adaptation. In all cases, the average rating response shifted toward that of the unadapted category. The average rating for stimuli in the opposite category from that of the adaptor remained relatively unchanged. These results indicate that the entire category of the adapting stimulus changes as a function of selective adaptation and that the effect is not confined to stimuli near the phonetic boundary.     

Experimental measures and theoretical account of hue scaling as a function of luminance

Functions relating the magnitude of chromatic response to stimulus luminance were determined at the unique green and yellow wavelengths. These measured functions were used to account for the shift from a preponderance of green at low stimulus luminances to a preponderance of yellow at higher luminances, for a stimulus wavelength of 550 nm. The two hue magnitude functions were found to have the same power-law exponents, and the hue shift was due to the difference in thresholds between the two opponent-color systems.     

Identity adaptation is mediated and moderated by visualisation ability

Depending on the previous research one reads, face aftereffects may or may not partially transfer across viewpoints. Two experiments are reported that explore this face-identity aftereffect by varying the adaptor type. Adaptation occurs when different views of the identity are used and even when the person's name is the adaptor. Brief exposure or nationality did not produce adaptation. In a third experiment, the role of visualisation was explored. Participants with higher visualisation scores showed greater adaptation to names than those with lower scores. These findings suggest non-facial identity cues can lead to a facial adaptation effect and that visualisation may be the mechanism behind this.     

Susceptibility of a stop consonant to adaptation on a speech-nonspeech continuum: Further evidence against feature detectors in speech perception

The present experiment uses the perceptual adaptation paradigm to establish the validity of a previous test of the feature detector model of speech perception. In the present study, a synthetic stimulus series varied from a CV syllable, [ba], to a nonspeech buzz. When the endpoint tokens were employed alternatively as adaptors, the category boundary was shifted relative to unadapted identification in each adaptor condition. This result suggests that a prior test which used a vowel as the speech endpoint was legitimate because a stop consonant, an exemplary speech sound, was also susceptible to perceptual adaptation in a speech-nonspeech context. Feature detector models predict, incorrectly, that this outcome is impossible. Therefore, this finding may be taken to undermine the interpretation of adaptation as fatigue in a set of detectors tuned to detect the distinctive features of linguistic analysis.     

The effect of selective adaptation on the identification of speech sounds

An experiment was performed to determine the effect of selective adaptation on the identification of synthetic speech sounds which varied along the phonetic dimensionplace of articulation. Adaptation with a stimulus of a particular place value led to a reduction in the number of test stimuli identified as having that place value. An identification shift was obtained even when the acoustic information specifying place value for the adapting stimulus had virtually nothing in common with the information specifying place value for any of the test stimuli. Removing the vowel portion of an adapting stimulus eliminated identification shift only when the resulting stimulus was no longer perceived as speech-like. The results indicate that at least part of the adaptation effect occurs at a site of phonetic, not merely acoustic, feature analysis.

     

Scaling of saturation and hue in the nonspectral region

The saturation of two nonspectral hues, magenta and violet, and the hue shift between red and blue through the nonspectral region were both scaled by two methods, equisection to produce a difference scale, ψ_D, and ratio judgments to produce a magnitude scale, ψ_M. The colored stimuli were viewed through apertures in a dark surround, with the luminance kept constant at one of three levels, 0.5, 2.5, and 12.6 cd/m². As previously found with saturation and hue shift between two adjacent primary hues in the spectral region, WD was linear with colorimetric purity for the saturation of magenta or violet and with the mixture ratio of red or blue for the hue shift, whereas ψ_M was a power function of colorimetric purity for the saturations and of the mixture ratio for the hue shift with exponents larger than unity in both cases. The present results were combined with previous results to give the change of parameters for saturation functions over the entire hue circle.     

Color categories in macaques.

This experiment investigated whether macaque monkeys partition the photic spectrum into the same four basic hue categories that humans do, i.e., blue, green, yellow, and red. Monkeys were trained to respond in the presence of one chromatic stimulus and were tested, in extinction, for generalization to others. In extinction, the monkeys responded at similar and high levels to stimuli that fell in the same basic human hue category as the training stimulus and at similar and much lower levels to stimuli that fell in a different human hue category from the training stimulus. It was concluded that macaques and humans categorize the spectrum in a similar fashion.     

Some properties of linguistic feature detectors

A series of experiments, using a selective adaptation procedure, investigated some of the properties of the linguistic feature detectors that mediate the perception of the voiced and voiceless stop consonants. The first experiment showed that these detectors are centrally rather than peripherally located, in that monotic presentation of the adapting stimulus and test stimuli to different ears resulted in large and reliable shifts in the locus of the phonetic boundary. The second experiment revealed that the detectors are part of the specialized speech processor, inasmuch as adaptation of a voicing detector (as measured by a shift in the phonetic boundary) occurred only when the voicing information was presented in a speech context. In the third experiment, the detector mediating perception of the voiced stops was shown to be more resistant to adaptation than the detector mediating perception of the voiceless stops.     

Color vision and hue categorization in young human infants.

Two studies examined the organization of color perception in 4-month-old human infants. In Study 1, infants looked at selected spectral stimuli repeatedly until their visual attention waned. The stimuli represented instances of basic adult hue categories - blue, green, yellow, and red. Following habituation, infants were shown a series of wavelengths which were the same as or different from the stimuli first seen. Analyses of infant attention during this dishabituation phase of the study indicated that infants categorize wavelengths by perceptual similarity; that is, they see hues in the spectrum much as adults do. In Study 2, a group of infants who looked at the alteration of two wavelengths from the same hue category habituated as did the group of infants who looked at the repitition of a single wavelength from that category, but a group of infants who looked at two wavelengths from different categories habituated at a slower rate. Data from the two studies suggest a high degree of organization of the color world prior to language acquisition.     

A random-walk model of accuracy and reaction time applied to three experiments on pigeon visual discrimination

A random-walk model of visual discrimination is described and applied to reaction time (RT) distributions from three discrete-trial experiments with pigeons. Experiment 1 was a two-choice hue discrimination task with multiple hues. Choice percentages changed with hue discriminability; RTs were shortest for the least and most discriminable stimuli. Experiments 2 and 3 used go/no-go hue discriminations. Blocks of sessions differed in reward probability associated with a variable red stimulus in Experiment 2 and with a constant green stimulus in Experiment 3. Changes in hue had a large effect on response percentage and a small effect on RT; changes in reward shifted RT distributions on the time axis. The "random-walk, pigeon" model applied to these data is closely related to Ratcliff's diffusion model (Ratcliff, 1978; Ratcliff & Rouder, 1998). Simulations showed that stimulus discriminability affected the speed with which evidence accumulated toward a response threshold, in line with comparable effects in human subjects. Reward probability affected bias, modeled as the amount of evidence needed to reach one threshold rather than the other. The effects of reward probability are novel, and their isolation from stimulus effects within the decision process can guide development of a broader model of discrimination.     

Continuous dynamics of color categorization

In order to assess whether color categorization is sensitive to within-category differences in hue, we monitored mouse trajectories in a modified categorization task. Participants saw color swatches from a blue-green continuum and categorized them with a computer mouse by selecting one of two colored regions at the top of a monitor. An analysis of the mouse trajectories showed that the deviation toward the competing category was a function of hue: As hues approached the category boundary, they increasingly deviated to the competitor. This work presents evidence for parallel activation on the level of hue and category processing for color, as well as simultaneous activation of perceptually adjacent categories. Thus, a dynamic process sensitive to fine-grained within-category detail best characterizes color categorization.     

Color-naming functions for the pigeon

Six pigeons were trained to match wavelengths in a three-key matching-to-sample paradigm. Test trials were occasionally presented, where probe wavelengths appeared on the center key and choices were made to the training stimuli presented on the side keys. Color naming functions were obtained by plotting the percentage of test trials that each training stimulus wavelength was chosen for each center key probe wavelength. The wavelength where the functions intersected was interpreted as a transition point between pigeon hues. Three experiments employed different wavelengths as training stimuli. The first two experiments demonstrated that the intersection of the color-naming functions occurred in all cases at 540 nm and 595 nm. The third experiment employed 540 nm and 595 nm as two of the three training stimuli, and the relatively slow acquisition, together with the resulting color-naming functions, supported the proposition that 540 nm and 595 nm may be transition point wavelengths between pigeon hues.     

Transfer of hue matching in pigeons.

Pigeons were trained on a modified three-key matching-to-sample procedure, in which only one comparison key (rather than two) was lighted after an observing response to the center-key standard. Pecks on keys of matching comparison hues were reinforced. When non-matching hues appeared as the initially lighted comparisons, the nonmatching hue terminated and the matching hue appeared on the other side key only if the pigeon did not peck the nonmatching comparison for 4.8 sec. Pecks to the nonmatching hue reset the 4.8-sec delay interval. Three hues were used during acquisition. During transfer tests, two novel hues were substituted individually or together for one or two of the training hues. Latencies to the novel side-key hue were shortest when a novel matching hue appeared as the standard on the center key, and were essentially identical to baseline matching latencies. In contrast, when a novel hue appeared as either a standard or comparison in a nonmatching combination, latencies increased with increasing separation between the noevel hue and the nonmatching hue. These transfer data demonstrate the concept of hue matching.     

Color sensation of normal and anomalous trichromats measured by magnitude estimation

Summary Colors perceived by normal, protanomalous, and deuteranomalous trichromats were scaled by magnitude estimation. As a result, opponent-colors functions were obtained which show the hue sensations produced by spectral lights. For color-normal observers, the loci of maximal hue sensations were different in some aspects from those expected from current opponent-colors theories.The results obtained from the anomalous observers confirm the view that the causes of prot- and of deuteranomalous vision consist in reverse shifts of the long- and middle-wavelength cone sensitivities respectively. It was found that anomalous trichromats perceive less red in the violet spectrum than do normal subjects. This finding may be explained by the hypothesis that short-wave-length red is produced by a secondary maximum of the long-wavelength cone excitation. In the experiment, the main defect of anomalous trichromats, compared with normal subjects, consisted in the high instability of hue perception and hue recognition. This instability may be explained by an unfavorable signal/noise relation created by the similarity of the two long-wavelength receptor sensibilities in the anomalous red/green systems.     

Stimulus generalization from feeder to response key in the acquisition of autoshaped pecking

During autoshaping, a 6-second presentation of one stimulus and a variable time 30-second presentation of a second stimulus alternated in appearance on a pigeon key. Grain always was delivered for 3 seconds at the end of the first stimulus interval. In the first experiment, autoshaped pecking of the stimulus preceding grain delivery began much sooner when that stimulus was a black vertical line on a white background and the other stimulus was green than when the opposite stimulus arrangement was used. Because these two stimuli differed in form, hue, brightness, and similarity in hue and brightness to the illumination of the raised feeder, three subsequent experiments examined whether the differential speed of autoshaping in the two groups was due to a feature-positive, feature-negative effect, a preference for brighter over darker stimuli, a simple preference for white over green, or stimulus generalization from the brightness or hue of the illuminated, raised feeder to the stimulus on the key preceding grain delivery. The data from these experiments showed that the first autoshaped key peck was most likely to be made to the stimulus of the same hue as that illuminating the feeder, regardless of whether that stimulus was positively or negatively associated with grain delivery. At least under some conditions, therefore, stimulus-generalization mediated response transfer of pecking grain in the presence of the hue illuminating the feeder to pecking the key illuminated by a similar hue appears to account for the occurrence of autoshaped key pecking.     

Processing of place information in stop consonants

One of the basic questior, s that models of speech perception must answer concerns the conditions under which various cues will be extracted from a stimulus and the nature of the mechanisms which mediate this process. Two selective adaptation experiments were carried out to explore this question for the phonetic feature of place of articulation in both syllableinitial and syllable-final positions. In the first experiment, CV and VC stimuli were constructed with complete overlap in their second- and third-formant transitions. Despite this essentially complete overlap, no adaptation effects were found for a VC adaptor and a CV test series (or vice versa). In the second experiment, various vowel, vowel-like, and VC-like adaptors were used. The VC-like adaptors did have a significant effect on the CV category boundary, while the vowel and vowel-like stimuli did not. These results are interpreted within both one- and twolevel models of selective adaptation. These models are distinguished by whether selective adaptation is assumed to affect a single auditory level of processing or to affect both an auditory level and a later phonetic level. However, both models incorporate detectors at the auditory level which respond whenever particular formant transitions are present. These auditory detectors are not sensitive to the position of the consonant transition information within the syllable.     

Developmental color perception.

The purpose of this research is to extend the investigation of surface color perception to several age levels. The 108-item color perception test, originally used with young children, employs six Munsell hue matrices divided into nine combinations each of low, mid, and high chroma and low, mid, and high value across two levels of hue difficulty. The pattern of error results are the same across the age groups comprising kindergartners, fifth graders, high school sophomores, nonartist adults, and professional artists: the lower the chroma and value, the higher the error rate; the higher the chroma and value, the lower the error rate. In hues, green and red are most difficult; orange and yellow are easiest. The frequency of error is linear with respect to age: the younger the group, the higher the error. The latency data differ with respect to age: adults are slowest, followed by kindergartners and fifth graders. High school sophomores are the fastest. The remaining latency results parallel the error results: the lower the chroma and value, the longer the latency and the more difficult the hue, the longer the latency. A set of surface color perception rules are generated.     

Scaling of saturation and hue

The study concerns the relation of saturation to the purity and luminance of aperture colors viewed in a dark surround. For the primary hues, red, yellow, green, and blue, and the intermediate hues, orange and yellowish green, the saturations increased as power functions of colorimetric purity. An IS-dB increase in luminance caused a threefold increase in the exponent for yellow, but luminance had little effect on the exponents of the other colors. The direct heterochromatic matching of saturation to saturation confirmed the validity of the scales determined by magnitude estimation and led to the construction of families of saturation scales based on a common unit called a crome. Equisection and jnd scales were also determined. Their nonlinearity suggests that saturation is a prothetic continuum. It was found that mixing red or green with yellow behaves much the same as mixing red or green with achromatic light. The changes in hue behave as prothetic continua, for the equisection and jnd scales are nonlinearly related to the power-function scales obtained by magnitude estimation and matching.     

A further parallel between selective adaptation and contrast

It is generally believed that selective adaptation effects in speech perception are due to a reduction in sensitivity of auditory feature detectors. Recent evidence suggest that these effects may derive instead from contrast. In a further test of the contrast hypothesis, we conducted two experiments each involving both adaptation and contrast sessions with matching stimulus sets. During the adaptation sessions of Experiment 1, subjects identified two series of velar stimuli varying in voice onset time, [ga]-[kha] and [gi]-[khi], before and after adaptation with of the following stimuli: [ga], [kha], [gi], and [khi]. In the contrast session, subjects identified either of two ambiguous test items (drawn from near the phonetic boundaries of the [ga]-[kha] and the [gi]-[khi] series) following a single presentation of [ga], [kha], [gi], or [khi]. For both the adaptation and contrast sessions, (a) the [--a] test items were more greatly affected (in a contrast direction) by the [--a] than by the [--i] adaptor/context stimuli, and (b) the [--i] test items were not differentially affected by the [--1] and [--i] adaptor/context stimuli. An analogous design was used in Experiment 2, except that the stimulus sets varied in pitch rather than vowel quality. For both the adaptation and contrast sessions, the test items were not differentially affected by the pitch of the adaptor/context stimulus. These parallel results provide further evidence that adaptation effects are actually a form of contrast.