Nominal Stimulus Research Articles

Electronically tunable immittances with applications to LP, BP, HP filter and VCO implementation

ABSTRACT Electronically tunable synthesis of immittances viz., inductor (L) and FDNR (D), using the voltage tunable current conveyor transadmittance amplifier (VTCCTA) block is presented. Design of selective LC and DR type resonators are derived. Subsequently, based on these resonators new VCO implementations, underlying the concept of short-circuit natural-frequency is proposed. According to this concept, second-order resonators yield a pair of imaginary-axis pole-pair; if Q~∞ this is amenable to sinusoid oscillator implementation without necessitating a nominal input stimulus (Vi ~0: short-circuit) to the resonator whereby the oscillation frequency (fo ) is the natural pole-frequency. To this end, both the LC and DR resonators may be utilised for the VCO design using a multiplication mode current conveyor (MMCC) element, of which the LC type follows a linear tuning law variable by a control voltage (Vd.c.). Experimental results with simulation and hardware-circuit test had been satisfactorily verified using standard commercially available IC-modules. Linear range of f o-variation upto 10 MHz with satisfactory phase noise-margin had been measured.

Mathematical learning theory through time

Stimulus sampling theory (SST: Estes, 1950, 1955a,b, 1959) was the first rigorous mathematical model of learning that posited a central role for an abstract cognitive representation distinct from the stimulus or the response. SST posited that (a) conditioning takes place not on the nominal stimulus presented to the learner, but on a cognitive representation caused by the nominal stimulus, and (b) the cognitive representation caused by a nominal stimulus changes gradually across presentations of that stimulus. Retrieved temporal context models assume that (a) a distributed representation of temporal context changes gradually over time in response to the studied stimuli, and (b) repeating a stimulus can recover a prior state of temporal context. We trace the evolution of these ideas from the early work on SST, and argue that recent neuroscientific evidence provides a physical basis for the abstract models that Estes envisioned more than a half-century ago.

Inflation Dynamics and Time-Varying Volatility: New Evidence and an Ss Interpretation *

Abstract Is monetary policy less effective at increasing real output during periods of high volatility than during normal times? In this article, I argue that greater volatility leads to an increase in aggregate price flexibility so that nominal stimulus mostly generates inflation rather than output growth. To do this, I construct price-setting models with “volatility shocks” and show these models match new facts in CPI micro data that standard price-setting models miss. I then show that these models imply that output responds less to nominal stimulus during times of high volatility. Furthermore, because volatility is countercyclical, this implies that nominal stimulus has smaller real effects during downturns. For example, the estimated output response to additional nominal stimulus in September 1995, a time of low volatility, is 55% larger than the response in October 2001, a time of high volatility.

Contralateral inhibition of distortion product otoacoustic emissions in children with auditory processing disorders

Objective: The purpose of this study was to evaluate changes in distortion product otoacoustic emission (DPOAE) level elicited by contralateral noise in children with normal hearing, and those with auditory processing disorders (APD) whose audiometric thresholds were normal. It was hypothesized that children with APD would demonstrate smaller changes. Design: Levels of DPOAEs were recorded for f2 stimulus tones fixed at 2, 3, and 4 kHz while the f1 tone was ramped around nominal stimulus frequency ratios of f2/f1 = 1.22 and 1.10. Mean and maximum absolute changes resulting from contralateral broadband noise presented at 60 dB SPL were evaluated across the DPOAE frequency bands for each individual and for both groups of subjects. Study sample: Eight normal-hearing children and eight children with APD whose audiometric thresholds were normal participated. Results: There were no significant differences in DPOAE inhibition between normal hearing and APD groups, or previously recorded adult data. Mean absolute changes were typically near 1 dB, except for f2 = 4 kHz and the stimulus frequency ratio 1.22 where inhibition was only 0.5 dB. However, there were individual children in both groups who demonstrated larger DPOAE changes for some stimulus parameters. Conclusions: The inhibition of otoacoustic emissions requires further study in APD children.SumarioObjetivo: El propósito de este estudio fue evaluar los cambios en el nivel de las emisiones otoacústicas por productos de distorsión (DPOAE) generados por ruido contralateral, en niños con audición normal y en aquellos con trastornos de procesamiento auditivo (APD), cuyos umbrales audiométricos era normales. Se planteó la hipótesis que los niños con ADP demostrarían cambios menores. Diseño: Se registraron los niveles de DPOAE para tonos de estímulo f2 fijos a 2, 3 y 4 KHz, mientras que el f1 fue colocado cercano a tasas nominales de frecuencia del estímulo f1/f2 = 1.22 y 1.10. Los cambios medios y máximos absolutos que resultaron del ruido de banda ancha contralateral a 60 dB SPL fueron evaluados en todas las bandas de frecuencias de las DPOAE para cada individuo y para ambos grupos de sujetos. Muestra del Estudio: Participaron ocho niños con audición normal y ocho niños con APD, cuyos umbrales audiométricos eran normales. Resultados: No hubo diferencias significativas en la inhibición de las DPOAE entre los grupos con audición normal y con APD, o con información de adultos previamente registrada. Los cambios medios absolutos estuvieron típicamente cerca de 1 dB, excepto para f2 = 4 kHz, para la tasa de frecuencia del estímulo de 1.22, donde la inhibición fue solo 0.5 dB. Sin embargo, hubo niños individuales en ambos grupos que demostraron cambios mayores en DPOAE para algunos parámetros de estímulo. Conclusiones: La inhibición de las emisiones otoacústicas requiere de más estudio en niños con APD.

Evaluative conditioning and the awareness issue: Assessing contingency awareness with the Four-Picture Recognition Test.

An experiment is described that tested the moderating influence of contingency awareness on evaluative conditioning. After participants were conditioned within the picture-picture paradigm, contingency awareness was assessed by means of a recognition test (i.e., the 4-picture recognition test). Results indicate an inverse relationship between the conditioned affective reaction and contingency awareness: Only participants classified as unaware in the recognition test showed significant effects of evaluative learning. A closer inspection indicates that aware individuals stored not only the valence but also the nominal stimulus in mind.

Dynamic accommodation responses to stationary colored targets.

When the targets or the background in a display are different colors, longitudinal chromatic aberration ensures that there is no single correct accommodative response. The purpose of the present study was to determine whether the response becomes more variable when viewing certain multicolor displays. Accommodative responses of five young participants were measured with a dynamic infrared optometer while they viewed steady targets at a nominal stimulus level of 3 D. Target-on-background color combinations were black on white, black on blue, black on red, blue on red, red on blue, dark blue on red, and dark red on blue. When compared with the standard black-on-white target, responses to targets with reduced spectral bandwidth were not significantly more variable. In most participants, responses to near-isoluminant targets (e.g., red on blue and blue on red) were not more variable than to the standard target. However, calculated confidence intervals cannot rule out moderate to large changes in variability near isoluminance. Responses to these multicolor targets tended to favor the blue focus. In most individuals, viewing multichromatic targets does not increase significantly the variation in accommodative response as compared with broadband black-and-white targets.

Frequency specificity of the human auditory brainstem and middle latency responses using notched noise masking.

This study investigated the frequency specificity of the auditory brainstem and middle latency responses to 80 and 90 dB ppe SPL 500-Hz and 90 dB ppe SPL 2000-Hz tonebursts. The stimuli were brief (2-1-2 cycle) linear-gated tonebursts. ABR/MLRs were recorded using two electrode montages: (1) Cz-nape of neck and (2) Cz-ipsilateral earlobe. Cochlear contributions to ABR wave V-Na and MLR waves Na-Pa and Pa-Nb were assessed by plotting notched noise tuning curves which showed amplitudes and latencies as a function of center frequency of the noise masker [Abdala and Folsom, J. Acoust. Soc. Am. 97, 2394 (1995); ibid. 98, 921 (1995)]. Maxima in the response amplitude profiles for the ABR and MLR to 80 dB ppe SPL tonebursts occurred within one-half octave of the nominal stimulus frequency, with minimal contributions to the responses from frequencies greater than one octave away. At 90 dB ppe SPL, contributions came from a slightly broader frequency region for both stimulus frequencies. Thus, the ABR/MLR to 80 dB ppe SPL tonebursts shows good frequency specificity which decreases at 90 dB ppe SPL. No significant differences exist in frequency specificity of: (1) ABR wave V-Na versus MLR waves Na-Pa and Pa-Nb at either stimulus frequency or intensity; and (2) ABR/MLRs recorded using the two electrode montages.

Contribution of various frequency bands to ABR in dolphins

Auditory brainstem responses (ABR) to clicks and noise bursts of various frequency bands and intensities were recorded in two bottlenosed dolphins, Tursiops truncatus. The purpose was to assess contributions of various parts of the cochlear partition to ABR and travelling wave velocity in the cochlea. At band-pass filtered stimuli (1–0.25 oct wide), ABR amplitude increased with increasing stimulus frequency, thus indicating higher contribution of basal cochlear parts. At high-pass and low-pass filtered stimuli, ABR amplitude increased with passband widening. However, the sum of all narrow-band contributions was a waveform of higher amplitude than the real ABR evoked by the wide-band stimulus. Applying a correction based on an assumption that the ‘internal spectrum’ is about 0.4 oct wider than the nominal stimulus spectrum resulted in the sum of narrow-band contributions equal to the wide-band ABR. The travelling wave velocity was computed based on ABR latencies and assigned a frequency of 128 kHz to the basal end of the cochlea. The computation gave values from 38.2 oct/ms at the proximal end of the basilar membrane to 4.0 oct/ms at a distance of 3.25 oct (13.5 kHz).

Frequency specificity of the human auditory brainstem and middle latency responses to brief tones. II. Derived response analyses.

This study investigated the frequency specificity of the auditory brainstem (ABR) and middle latency (MLR) responses to 500- and 2000-Hz brief tones using narrow-band derived response analyses of the responses recorded in high-pass masking noise [Oates and Stapells, J. Acoust. Soc. Am. 102, 3597-3608 (1997)]. Stimuli were linear- and exact-Blackman-gated tones presented at 80 dB ppe SPI. Cochlear contributions to ABR wave V-V' and MLR wave Na-Pa were assessed by response amplitude profiles as a function of derived band center frequency. The largest amplitudes of waves V and Na-Pa occurred in the 500- and 707-Hz derived bands in response to the exact-Blackman- and linear-gated 500-Hz tones. The peak in the response amplitude profiles for wave V to both 2000-Hz stimuli was seen in the 2000-Hz derived band. For wave Na-Pa, the maxima in the amplitude profiles occurred in the 2000- and 1410-Hz derived bands for the exact-Blackman- and linear-gated tones. Smaller cochlear contributions to the ABR/MLR were also present at 0.5-1 octave above and below the nominal stimulus frequencies. The ABR/MLR to 500- and 2000-Hz 80 dB ppe SPL tones thus shows good frequency specificity, with no significant differences in the frequency specificity of: (1) ABR versus MLR; (2) these evoked potentials to 500-versus 2000-Hz tones; and (3) responses to exact-Blackman- versus linear-gated tones.

The Generative Effects of Instructional Organizers with Computer-Based Interactive Video

Sixty-one nursing students and faculty were studied to compare the use of participatory graphic organizers to final form graphic organizers and advance organizers as adjunct instructional aids for computer-based interactive video. The participatory form was hypothesized to be more representative of Wittrock's generative learning hypothesis. The more generative form was thought to engage the learner in a more active, overt learning activity than the other two forms, which depend upon their nominal stimulus characteristics for effect and, therefore, to be more effective in assisting the learning and retention of the program material. Results did not support this hypothesis. The participatory group actually achieved the lowest mean scores. Moreover, the difference between the mean scores of the final form and participatory graphic organizer treatment groups was statistically significant at the p ≤ 0.01 level on both posttests. Interview data indicated the effectiveness of the final form graphic organizer treatment likely derived from the guided discovery approach of the CBIV program which appeared to cause considerable learner disorientation. The final form graphic organizer contained specific information to allow that treatment group to successfully navigate the disorienting sequences and to concentrate more fully on the content of the program.

Auditory nerve fiber responses predict the discriminability of VOT syllables

Responses of chinchilla auditory nerve fibers to synthesized syllables differing in VOT were obtained. A continuum heard as /da/∼/ta/ was used. Many neurons responded with an increase in average discharge rate or with a change in synchronized response whose latency matched the nominal stimulus VOT. Response latency was treated as a random variable. For each VOT pair, a statistic analogous to d' was calculated from the distribution of the difference between two random variables. Thresholds for ΔVOT were interpolated from psychometric functions based on this statistic. Thresholds were lowest for standard VOTs of 30–40 ms, but were highly dependent on the direction of change from the standard. These characteristics were also typical of the chinchilla's psychophysical thresholds for ΔVOT, reported by Kuhl [J. Acoust. Soc. Am. 70, 340–349 (1981)]; in addition, the quantitative agreement between neural and behavioral thresholds was usually very good. For this VOT continuum, discriminability reflects the precision of stimulus coding at the level of the auditory nerve. [Work supported by NINCDS.]

Objective Identification of Functional Units of Short-term Memory

The idea of functional memory units may, without exaggeration, be called the central aspect of any theory concerning the training and organization of memory. It was introduced to distinguish between the nominal elements, i.e., the elements presented for memorization, of the content of a stimulus and their internal representations. The elements of a series presented by an experimenter are often apprehended and remembered as parts of larger units. One functional unit may combine two or more elements of a series to be memorized, and the key to its recall will then be only a part of the nominal stimulus (Miller, 1964; Klatsky, 1978; Underwood, 1963; Mandler, 1967; Bower, 1977; et al.).

Depth of processing reexamined: The effects of the precision of encoding and test appropriateness

Two experiments examined the effects of level of processing and uniqueness of encoding on the ability to recognize the nominal stimulus among either sematically similar or structurally similar distractor items. Experiment 1 showed that semantic acquisition was superior to structural (case) acquisition given a semantically oriented recognition test, but that case acquisition was superior to semantic acquisition given a case oriented recognition test. Experiment 2 demonstrated that contrary to other reports, uniqueness as defined by the number of similarly encoded items affects nonsemantic as well as semantic modes of processing. The results favor a “precision of encoding” framework over one of “levels of processing.”

Convergence‐divergence and the learning of concrete and abstract sentences

School pupils (mean age 17 years) were classified as convergers or divergers on the basis of their performance on the AH5 Intelligence Test and the Uses of Objects test. They were presented with a set of concrete and abstract sentences, followed immediately by a forced‐choice recognition test. There was a significant interaction between abstractness‐concreteness and convergence‐divergence, in which the effect of the abstractness‐concreteness variable was highly significant for convergers, but was non‐significant for divergers. This interaction was attributed to the superior ability of divergers to discover those different interpretations of a single nominal stimulus held to be inherent in abstract, though not in concrete, sentences. In addition, some evidence against Paivio's (1971) dual‐coding model was presented.

The effect of constant vs. varied encoding and massed vs. distributed presentations on recall of paired associates

The variables of coding (constant vs. varied) and spacing (massed vs. distributed) were factorially combined in an independent-groups design. Sixteen nominal pairs were presented twice, with the two presentations being either massed or distributed. A given nominal pair (e.g., AR-LE) was accompanied either by the same word-pair code on both presentations (e.g.,arm-leg) or by a different code on each presentation (e.g.,arm-leg; arrive-leave). On a subsequent recall test, the nominal stimulus only was shown. Better recall of the nominal response was found after constant coding and after distributed presentations, and there was no interaction between the spacing and coding variables. The results (a) support none of the current proposed explanations for the distributed practice effect, and (b) suggest that the critical factor in determining the probability of response recall is the strength of the strongest potential route to the response, not the number of different routes. This research was supported by a grant from the Graduate School of the University of Wisconsin.

Stimulus encoding and the relationship between stimulus recognition and association formation

Four experiments investigated the relation between stimulus recognition and association formation. Subjects learned to associate trigram-digit or trigram-word pairs by either study-associative matching or study-recall procedures. Following training, subjects were given a stimulus recognition and matching or recall task. Stimulus recognition was facilitated when the trigrams were paired with representative words but not with digit responses. The probability of response recall, given nonrecognition of the stimulus, was above chance with the trigram-word pairs but not with the trigram-digit pairs, suggesting that subjects need only to retrieve an encoded version of the nominal stimulus in order to have access to response recall.

Organizational factors in memory

The research reviewed illustrates how the structural organization of material influences the way in which it is learned and recalled by the person. Specific factors investigated concerned relational rules and perceptual-conceptual groupings as these appeared in various laboratory learning tasks. The influence of relational rules was illustrated in paired-associate learning in which a list rule, stipulating a particular relation between the nominal stimulus and response terms, enhanced performance and reduced interference from other learning. The apparent role of the S-R pairing rule, inferred from studies of rhyming rules, is to enable restriction of the range of response alternatives which the person needs to consider at crucial points in his recall. The role of perceptual groupings was examined in immediate recall of digit series; conceptual groupings were examined in free recall of word lists. By one or another means, the learning materials are segmented by the subject into integrated groups which become his functional recall units. Recall suffers if the subject is made to adopt new groupings of the same material. The results on digit series were interpreted by the “reallocation” hypothesis, which ties together the perceptual coding of a string and the “memory location” at which its trace is stored, with implications about recognition memory and trial-by-trial increments in recall of the same string. In free recall, the stable groupings of list words which develop are often supplemented by the subject developing a higher-order retrieval scheme to guide his reproduction of the many items on the list. The nature and influence of several retrieval schemes is reviewed, including interchunk associations, pegword mnemonics, semantic category cuing, and hierarchically embedded category systems. These basic schemes provide implicit cues to guide the person's search through memory. Hierarchical schemes, based on recursive associative decoding, are particularly effective retrieval plans. The results are discussed in terms of the advantages of common strategies preferred by human learners, viz., the tendency to subdivide and group material, and to do this recursively, producing a hierarchical organization of the information to be learned.

Stimulus encoding as a determinant of retroactive inhibition

It was hypothesized that unlearning would be reduced if S s were able to encode differentially the nominal stimulus terms in the first and second lists in the A-B, A-C (AC) paradigm, presumably due to a decrease in the amount of first-list response elicitation during second-list learning. By employing compound-trigram stimuli and a manipulation of initial-letter overlap of responses and different stimulus components, conditions were established which were expected to provide for high (H) or low (L) opportunity for differential stimulus encoding in the AC paradigm and in the A-B, D-C (DC) paradigm. Under L conditions unlearning was inferred in the AC paradigm, since first-list recall was poorer than that in the DC paradigm. There was no evidence for unlearning in the AC paradigm under H conditions. Under all conditions, degree of second-list learning had no reliable effect on first-list recall except over the first two trials.

Stimulus selection as a function of letter color

A PA list comprised of nonoverlapping consonant-trigram stimuli with numerals as responses was presented to three groups of Ss. For a given group, the letters in either the initial, medial, or final position of the trigrams were red, while the letters in the other two positions were black. When this list had been learned to criterion, the individual letters were presented and the Ss were required to respond with the appropriate number. The groups showed nonsignificant differences in the rate of learning the PA list. In the transfer test, Ss responded correctly more often to the letters which had been red in the PA list. The results were interpreted as indicating that Ss will tend to utilize a single distinctive element of a multiple-element nominal stimulus as the functional stimulus.

Stimulus selection at different stages of paired-associate learning.

Ss learned paired associates with compound stimuli (word + nonsense). Transfer was tested to individual components after varying amounts of training on the compounds. Ss who were trained to a single perfect trial showed no more transfer to nonsense components than Ss trained to 4 of 8 correct responses to the compounds; however, Ss receiving 10 overtraining trials on compounds showed substantially more transfer to the nonsense components. Then a group of Ss was given training after learning a list of compound stimuli to criterion, but during the extended training other items were added so that the list was not mastered while the initial items were receiving overtraining. This group showed no more transfer to nonsense components than a group trained just to criterion. The data are generally consistent with the hypothesis that Ss actively select among stimulus aspects until the list is mastered, and then relax the selection of attention during overtraining. It can be accepted now that when stimuli of paired associates are complex, 5s often learn pairs by associating the response with a part of the stimulus. Underwood (1963) reviewed several items of evidence and concluded that £s carry on a process of stimulus selection, thereby producing a disparity between the nominal stimulus (presented by E} and the functional stimulus (with which associates the response). Since Underwood's review, further studies by Newman and Taylor (1963), Jenkins and Bailey (1964), Cohen and Musgrave (1964), and Houston (1964) all have provided further demonstrations that after learning a list of pairs with complex stimuli, there are cases in which 5 can give the correct response to one element of a stimulus compound but not to another.