The role of phonemes and syllables in the perceived similarity of speech sounds for children

In two experiments, we investigated the factors that influence the perceived similarity of speech sounds at two developmental levels. Kindergartners and second graders were asked to classify nonsense words, which were related by syllable and phoneme correspondences. The results support the existence of a developmental trend toward increased attention to individual phonemic segments. Moreover, one significant factor in determining the perceived similarity of speech sounds appears to be the position of the component correspondences; attention to the beginning of utterances may have developmental priority. An unexpected finding was that the linguistic status of the unit involved in a correspondence (whether it was a syllable or a phoneme) did not seem particularly important. Apparently, the factors which contribute to the perceived similarity of speech sounds in the classification task are not identical to those which underlie performance in explicit segmentation and manipulation tasks, since in the latter sort of task, syllables are more accessible than phonemes for young children. The present task may tap a level of processing that is closer to the one entailed in word recognition and lexical access.     

Adults’ perception of native and nonnative vowels: Implications for the perceptual magnet effect

Two experiments were conducted to evaluate the perceptual magnet effect. In Experiment 1, Amer-ican English speakers representing diverse dialects were presented with a fine-grained set of stimuli (varying in just noticeable differences forF1 andF2) and indicated whether they heard “/i/” or “not /i/,” thus delimiting the /i/ portion of the vowel space for individual subjects. Then these same subjects selected their own /i/ prototype with a method-of-adjustment procedure. The data from this experiment were used to synthesize customized prototype and nonprototype stimulus sets for Experiment 2. In Experiment 2,24 of our original 37 subjects completed a discrimination task for each of three conditions, in which vector stimuli varied from the subject’s prototype, the nonprototype, or a foreign vowel (/y/) in 15-mel steps. Subjects displayed higher discrimination, as indexed byd′, for the nonprototype condition than they did for both the prototype and the foreign conditions. In addition, discrimination was better for variants further away from the referent in each condition. However, discrimination was not especially poor for stimuli close to subjects’ individual prototypes—a result that would have yielded the strongest support for the operation of a magnet effect. This negative finding, together with other aspects of our results, raises problems for any theory of vowel perception that relies solely on “one-size-fits-all” prototype representations.     

Young children’s age-of-acquisition estimates for spoken words

This study was concerned with the impact of stimulus familiarity on young children's ability to recognize spoken words and make explicit judgments about them. In Experiment 1, 5-year-olds made age-of-acquisition (AOA) estimates for a set of words that were very similar to estimates made by older children and adults. In Experiment 2, young children's picture recognition, mispronunciation detection, and vocabulary monitoring performance all varied systematically with these AOA estimates and with a stimulus-type (intact-mispronounced) manipulation. Subjective AOA estimates (whether from children or from adults) proved to be a better predictor of performance than did two objective familiarity measures and subjective imageability. These results point to considerable metalexical knowledge on the part of young children or explicit sensitivity regarding their own vocabulary knowledge. In addition, the results lend some support to the notion that actual AOA contributes to subjective AOA estimates.     

The gating paradigm: Effects of presentation format on spoken word recognition by children and adults

This study focused on the impact of stimulus presentation format in the gating paradigm with age. Two presentation formats were employed—the standard, successive format and a duration-blocked one, in which gates from word onset were blocked by duration (i.e., gates for the same word were not temporally adjacent). In Experiment 1, the effect of presentation format on adults’ recognition was assessed as a function of response format (written vs. oral). In Experiment 2, the effect of presentation format on kindergarteners’, first graders’, and adults’ recognition was assessed with an oral response format only. Performance was typically poorer for the successive format than for the duration-blocked one. The role of response perseveration and negative feedback in producing this effect is considered, as is the effect of word frequency and cohort size on recognition. Although the successive format yields a conservative picture of recognition, presentation format did not have a markedly different effect across the three age levels studied. Thus, the gating paradigm would seem to be an appropriate one for making developmental comparisons of spoken word recognition.     

Adults' perception of native and nonnative vowels: implications for the perceptual magnet effect.

Two experiments were conducted to evaluate the perceptual magnet effect. In Experiment 1, American English speakers representing diverse dialects were presented with a fine-grained set of stimuli (varying in just noticeable differences for F1 and F2) and indicated whether they heard "/i/" or "not/i/," thus delimiting the /i/ portion of the vowel space for individual subjects. Then these same subjects selected their own /i/ prototype with a method-of-adjustment procedure. The data from this experiment were used to synthesize customized prototype and nonprototype stimulus sets for Experiment 2. In Experiment 2, 24 of our original 37 subjects completed a discrimination task for each of three conditions, in which vector stimuli varied from the subject's prototype, the nonprototype, or a foreign vowel (/y/) in 15-mel steps. Subjects displayed higher discrimination, as indexed by d', for the nonprototype condition than they did for both the prototype and the foreign conditions. In addition, discrimination was better for variants further away from the referent in each condition. However, discrimination was not especially poor for stimuli close to subjects' individual prototypes--a result that would have yielded the strongest support for the operation of a magnet effect. This negative finding, together with other aspects of our results, raises problems for any theory of vowel perception that relies solely on "one-size-fits-all" prototype representations.     

Methylphenidate, amygdalectomy, and active avoidance performance in the rat

Amygdalectomized and control rats were given 400 active avoidance training trials in a shuttle box. Control animals received 0, 4, 8, or 16 mg/kg of methylphenidate throughout acquisition. Amygdalectomized animals were given the first 200 trials without drug, followed by 200 trials with drug. The administration of methylphenidate produced an abrupt and large improvement in performance in the amygdalectomized animals. One month after acquisition under the drug, retraining without drug revealed a significant retention effect for the three amygdaloid-drug groups relative to the nondrug-amygdaloid group. These results indicate that although amygdalectomy impairs the performance of avoidance responses, it does not prevent the learning or retention of such responses. Since methylphenidate appears to act primarily on dopaminergic mechanisms, the possible influence of amygdalectomy on such mechanisms is discussed.     

Imitation of Self‐Aggressive Behavior: An Experimental Test of the Contagion Hypothesis1

The purpose of the present study was to experimentally examine the influence of a self‐aggressive model on self‐aggressive behavior under controlled laboratory conditions. Participants (N= 94) were given the opportunity to self‐administer electric shock while competing with a fictitious opponent in a reaction‐time task. Participants observed the opponent self‐administer either increasingly intense shock (a self‐aggressive model) or constant low shocks (a non‐self‐aggressive model). Self‐aggression was defined as the intensity of shock that was self‐administered by participants. Results provide support for the notion that social information can influence the expression of self‐aggressive behavior. Specifically, participants attended to the opponent's shock choices in both model conditions, and chose shocks consistent with those of the observed model.