Arturo Camacho

Horseradish peroxidase study in rat of the neural connections of the organum vasculosum of the lamina terminalis

Using highly localized injections by a transbuccal approach a study of the afferent and efferent connections of the organum vasculosum laminae terminalis (OVLT) with horseradish peroxidase (HRP) methods was carried out. The results showed that the OVLT has direct connections to several hypothalamic nuclei (anterior, preoptic, lateral preoptic, ventromedial nucleus) and to extrahypothalamic (central gray, locus coeruleus, subfornical organ) regions. There was not a direct projection from the supraoptic nucleus. Some of these connections may be involved in the functional actions of the OVLT observed after central injections of angiotensin II.

Cholinergic stimulation of hippocampal pyramidal cells is inhibited by increasing membrane cholesterol

Abstract Carbachol is known to stimulate pyramidal cells in the CA1 region of hippocampal slices. The incorporation of cholesterol by perfusion of slices with cholesterol-containing buffer abolishes the carbachol response. The response returns upon removal of cholesterol. Changes in neuronal membrane properties could contribute to alterations in cholinergic transmission thought to occur in senile dementia and chronic alcoholism.

A Pitch Estimation Algorithm Based on the Smooth Harmonic Average Peak-to-Valley Envelope

We propose SHAPE, a novel pitch estimation algorithm (PEA) that builds upon previous PEAs, addressing and solving some of their limitations. The SHAPE algorithm estimates the pitch using a smooth function to compute the average peak to valley distance at harmonic locations. This is done by performing an integral transform over the square-root magnitude of the spectrum using a truncated decaying cosine as a kernel. SHAPE was designed to both match human perception particularly for inharmonic sounds and to be competitive with numerous other PEAs as demonstrated on a common database.

Computing pitch of speech and music using a sawtooth waveform inspired pitch estimator

A powerful pitch estimation algorithm called SWIPE has been developed for processing speech and music. SWIPE is shown to outperform existing algorithms on several publicly available speech and musical instrument databases, and a disordered speech database, reducing the gross error rate by 40%, relative to the best competing algorithm. In short, SWIPE estimates the pitch as the fundamental frequency of a sawtooth waveform, whose spectrum best matches the spectrum of the input signal. The short‐time Fourier transform of the sawtooth waveform provides an extension to older frequency‐based, sieve‐type estimation algorithms by providing smooth peaks with decaying amplitudes to correlate with the fundamental frequency (if present) and its harmonics. An improvement on the algorithm is achieved by using only the first and prime harmonics, which significantly reduces subharmonic errors commonly found in other pitch estimation algorithms.

Autonomous detection of neotropical sciaenid fishes

Sciaenid passive acoustics are a demonstrated valuable tool for fisheries management. In spite of this, an efficient software tool to detect and identify fish sounds is not currently available. Such tool would be useful for autonomous recognition and array methodologies. For Neotropical environments this lack is even more conspicuous since the availability of corroborated sciaenid sounds is limited. We are developing such tools using corroborated Cynoscion squamipinnis (Pisces: Sciaenidae) sounds. Our approach is based on timbre statistics, short and long-term partial loudness, and the 30 Hz typical pattern found on the signals stridulations. Relevant fish drums are detected through empirically found fix thresholds for the timbre statistics and the 30 Hz pattern, and a dynamic threshold established by an unsupervised algorithm based on the long-term loudness. Current results show a recognition rate of 80%. Despite these promising numbers, there are still challenges ahead. In the future, we plan to incorp...

Evaluating a model to estimate breathiness in vowels

The perception of breathiness in vowels is cued by changes in aspiration noise (AH) and the open quotient (OQ) [Klatt and Klatt, J. Acoust. Soc. Am. 87(2), 820–857 (1990)]. A loudness model can be used to determine the extent to which AH masks the harmonic components in voice. The resulting partial loudness (PL) and loudness of AH (noise loudness; NL) have been shown to be good predictors of perceived breathiness [Shrivastav and Sapienza, J. Acoust. Soc. Am. 114(1), 2218–2224 (2005)]. The levels of AH and OQ were systematically manipulated for ten synthetic vowels. Perceptual judgments of breathiness were obtained and regression functions to predict breathiness from NL/PL were derived. Results show breathiness to be a power function of NL/PL when NL/PL is above a certain threshold. This threshold appears to be affected by the stimulus pitch. A second experiment was conducted to determine if the resulting power function could be used to estimate breathiness in natural voices. The breathiness of novel stimu...

Automatic detection of vocalizations of the frog Diasporus hylaeformis in audio recordings

A method for the automatic detection of calls of the frog Diasporus hylaeformis (Eleutherodactylidae) in audio recordings is proposed. The method uses the loudness, timber, and pitch of the vocalizations to identify the calls of the most prevalent individual in a recording. The first step consists in calculating the loudness of the signal to recognize the sections where the focal individuals vocalizations are. The second step consists in using the timber of the signal to recognize vocalizations. Finally, we use two principles we observed in the sounds produced by this species to discriminate between the calls of the most prevalent individual and other calls: individuals tend to vocalize using an almost constant pitch and different individuals use different pitches. Results show that the method is resistant to background noise (including calls of individuals of the same species), microphone-manipulation-induced noise, and human voice, and also that it adapts well to variations in the microphone level prod...

Predicting changes in breathiness resulting from variations in aspiration noise and open quotient using a loudness model

Previous studies have reported that increases in high‐frequency aspiration noise (AH) and open quotient (OQ) are correlated with an increase in the perception of breathiness in vowels [Klatt and Klatt, J. Acoust. Soc. Am. 87, 820–857 (1990)]. However, a system based on psychoacoustic loudness models has been shown to predict the level of breathiness in vowels to a greater extent than AH and OQ themselves [Shrivastav and Sapienza, J. Acoust. Soc. Am. 114, 2217–2224 (2003)]. The goal of this experiment was to verify the significance of AH and OQ in the perception of breathiness and to determine how each of these influences the output of the loudness model, individually and in combination. Ten vowels, five male and five female, were synthesized using a Klatt synthesizer. Each vowel was used to generate three continua varying in terms of their OQ and/or AH. Ten listeners rated breathiness for each continuum using a magnitude estimation task. Results show that normalized partial loudness as well as the loudnes...

Automatic recognition of accessible pedestrian signals

Accessible pedestrian signals (APS) enhance accessibility in streets around the world. Recent attempts to extend the use of APS to people with visual and audible impairments have emerged from the area of audio signal processing. Even though few authors have studied the recognition of APS by sound, comprehensive literature in Biology have been published for recognizing other simple sounds like bird and frog calls. Since these calls exhibit the same periodic and modulated nature as APS, many of the existent approaches can be adapted for this purpose. We present an algorithm that uses the mentioned approach. The algorithm was evaluated using a collection of 79 recordings gathered from streets in San Jose, Costa Rica, where the solution will be implemented. Three types of sounds are available: a low-pitch chirp, a high-pitch chirp and, a cuckoo-like. The results showed a precision of 87%, a specificity of 83%, a sensibility of 86%, and a F-measure of 85%.

Automatic manatee count using passive acoustics

The West Indian manatee is a threatened species throughout its known range. To improve its conservation, it is necessary to locate and count the individuals. This is a very difficult task due to the cryptic behavioral characteristics of the species and the environmental constrains, particularly in the Central American region, where muddy waters produce limited visibility. A method to estimate manatee population through vocalizations is a reliable, inexpensive, non-invasive, and novel option in the region. Digital signal processing techniques are proposed to identify individuals in field recordings of manatee vocalizations. The proposed methods for signal denoising and vocalization recognition have produced promising results. Further work needs to be done to identify individuals.