PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 8326063

Analyzing and modeling fractal intensity point processes.

A R Kumar·D H Johnson
View original source ↗Export metadata ↓

Abstract

Fractal intensity point processes--doubly stochastic point processes with a fractal waveform intensity process--are required to describe the discharge patterns recorded from the auditory and visual systems. The Fano factor--the ratio of the variance of the number of events in an interval to the mean of this number--captures the self-similar characteristics of the intensity via two quantities: fractal dimension and fractal time. The fractal dimension is the exponent of the asymptotic power law behavior of the Fano factor with interval duration. The fractal time delineates long-term fractal behavior from short-term characteristics of the data. The average rate and self-similarity parameter of the intensity process, absolute and relative refractory effects, and serial dependence all modify the fractal time. To generate fractal intensity point processes, stochastic fractal processes are derived by applying memoryless, nonlinear transformations to fractional Gaussian noise. The intensity's amplitude distribution in combination with the Fano factor form criteria to choose the transformation that best describes data.

Explore related subjects

Auditory PerceptionFemaleHumansMaleModels, NeurologicalNeural ConductionNoiseStochastic ProcessesVestibulocochlear NerveJournal ArticleResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A R Kumar, D H Johnson. 1993. Analyzing and modeling fractal intensity point processes.. https://doi.org/10.1121/1.405692

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2007

Hearing lips and seeing voices: how cortical areas supporting speech production mediate audiovisual speech perception.

Observing a speaker's mouth profoundly influences speech perception. For example, listeners perceive an "illusory" "ta" when the video of a face producing /ka/ is dubbed onto an audio /pa/. Here, we show how cortical areas supporting speech production mediate this illusory percept and audiovisual (AV) speech perception more generally. Specifically, cortical activity during AV speech perception occurs in many of the same areas that are active during speech production. We find that different perceptions of the same syllable and the perception of different syllables are associated with different distributions of activity in frontal motor areas involved in speech production. Activity patterns in these frontal motor areas resulting from the illusory "ta" percept are more similar to the activity patterns evoked by AV(/ta/) than they are to patterns evoked by AV(/pa/) or AV(/ka/). In contrast to the activity in frontal motor areas, stimulus-evoked activity for the illusory "ta" in auditory and somatosensory areas and visual areas initially resembles activity evoked by AV(/pa/) and AV(/ka/), respectively. Ultimately, though, activity in these regions comes to resemble activity evoked by AV(/ta/). Together, these results suggest that AV speech elicits in the listener a motor plan for the production of the phoneme that the speaker might have been attempting to produce, and that feedback in the form of efference copy from the motor system ultimately influences the phonetic interpretation.

Auditory Perception↗
PubMed2006

Top-down processes during auditory phoneme categorization in dyslexia: a PET study.

While persistence of subtle phonological deficits in dyslexic adults is well documented, deficit of categorical perception of phonemes has received little attention so far. We studied learning of phoneme categorization during an activation H(2)O(15) PET experiment in 14 dyslexic adults and 16 normal readers with similar age, handedness and performance IQ. Dyslexic subjects exhibited typical, marked impairments in reading and phoneme awareness tasks. During the PET experiment, subjects performed a discrimination task involving sine wave analogues of speech first presented as pairs of electronic sounds and, after debriefing, as syllables /ba/ and /da/. Discrimination performance and brain activation were compared between the acoustic mode and the speech mode of the task which involved physically identical stimuli; signal changes in the speech mode relative to the acoustic mode revealed the neural counterparts of phonological top-down processes that are engaged after debriefing. Although dyslexic subjects showed good abilities to learn discriminating speech sounds, their performance remained lower than those of normal readers on the discrimination task over the whole experiment. Activation observed in the speech mode in normal readers showed a strongly left-lateralized pattern involving the superior temporal, inferior parietal and inferior lateral frontal cortex. Frontal and parietal subparts of these left-sided regions were significantly more activated in the control group than in the dyslexic group. Activations in the right frontal cortex were larger in the dyslexic group than in the control group for both speech and acoustic modes relative to rest. Dyslexic subjects showed an unexpected large deactivation in the medial occipital cortex for the acoustic mode that may reflect increased effortful attention to auditory stimuli.

Auditory Perception↗