Pitch then power: limitations to acceleration in quadrupeds

Rapid acceleration and deceleration are vital for survival in many predator and prey animals and are important attributes of animal and human athletes. Adaptations for acceleration and deceleration are therefore likely to experience strong selective pressures—both natural and artificial. Here, we explore the mechanical and physiological constraints to acceleration. We examined two elite athletes bred and trained for acceleration performance (polo ponies and racing greyhounds), when performing maximal acceleration (and deceleration for ponies) in a competitive setting. We show that maximum acceleration and deceleration ability may be accounted for by two simple limits, one mechanical and one physiological. At low speed, acceleration and deceleration may be limited by the geometric constraints of avoiding net nose-up or tail-up pitching, respectively. At higher speeds, muscle power appears to limit acceleration.     

Processing of abstract rule violations in audition

The ability to encode rules and to detect rule-violating events outside the focus of attention is vital for adaptive behavior. Our brain recordings reveal that violations of abstract auditory rules are processed even when the sounds are unattended. When subjects performed a task related to the sounds but not to the rule, rule violations impaired task performance and activated a network involving supratemporal, parietal and frontal areas although none of the subjects acquired explicit knowledge of the rule or became aware of rule violations. When subjects tried to behaviorally detect rule violations, the brain's automatic violation detection facilitated intentional detection. This shows the brain's capacity for abstraction - an important cognitive function necessary to model the world. Our study provides the first evidence for the task-independence (i.e. automaticity) of this ability to encode abstract rules and for its immediate consequences for subsequent mental processes.     

Individual Differences in the Frequency-Following Response: Relation to Pitch Perception

The scalp-recorded frequency-following response (FFR) is a measure of the auditory nervous system’s representation of periodic sound, and may serve as a marker of training-related enhancements, behavioural deficits, and clinical conditions. However, FFRs of healthy normal subjects show considerable variability that remains unexplained. We investigated whether the FFR representation of the frequency content of a complex tone is related to the perception of the pitch of the fundamental frequency. The strength of the fundamental frequency in the FFR of 39 people with normal hearing was assessed when they listened to complex tones that either included or lacked energy at the fundamental frequency. We found that the strength of the fundamental representation of the missing fundamental tone complex correlated significantly with people''s general tendency to perceive the pitch of the tone as either matching the frequency of the spectral components that were present, or that of the missing fundamental. Although at a group level the fundamental representation in the FFR did not appear to be affected by the presence or absence of energy at the same frequency in the stimulus, the two conditions were statistically distinguishable for some subjects individually, indicating that the neural representation is not linearly dependent on the stimulus content. In a second experiment using a within-subjects paradigm, we showed that subjects can learn to reversibly select between either fundamental or spectral perception, and that this is accompanied both by changes to the fundamental representation in the FFR and to cortical-based gamma activity. These results suggest that both fundamental and spectral representations coexist, and are available for later auditory processing stages, the requirements of which may also influence their relative strength and thus modulate FFR variability. The data also highlight voluntary mode perception as a new paradigm with which to study top-down vs bottom-up mechanisms that support the emerging view of the FFR as the outcome of integrated processing in the entire auditory system.     

Fear influences perceived reaching to targets in audition,but not vision

The superordinate mechanism view of emotions predicts that fear should influence perception to carry out the evolved function of overcoming immediate threats. Previous work demonstrates that fear does adaptively influence visual perception. However, there are recurring situations in which auditory perception is used for overcoming immediate threats (e.g., avoiding predators after dark). Some research suggests that the auditory system, independent of fear, is adaptively biased to hear approaching sounds as closer than equidistant receding sounds (a.k.a. the looming bias). The present study investigated whether fear, as a superordinate mechanism, influences auditory perception such that sounds are perceived to be closer, ultimately providing an advantage when avoiding immediate threats. Participants judged whether or not they could reach to an aurally or visually perceived target while either in a fearful or neutral state. The results demonstrated that while in a fearful state, participants judged targets to be closer to them, but only when the target was perceived aurally. This finding extends previous work on adaptive biases in auditory perception to include the influence of fear.     

Foraging ecology and audition in echolocating bats

The types of echolocation signal and the auditory capacities of echolocating bats are adapted to specific acoustical constraints of the foraging areas. Bats hunting insects above the canopy use low frequencies for echolocation; this is an adaptation to prey detection over long distances. Bats foraging close to and within foliage avoid masking of insect echoes by specializing on 'fluttering target' detection. 'Gleaning' bats are adapted to the auditory detection of very faint noises generated by ground-dwelling prey, and are capable of analysing fine changes in the echo spectrum, which may indicate a stationary prey changing its posture on a substrate. This review of recent research demonstrates that, in bats, foraging ecology and audition are intricately interrelated and interdependent.     

Unicyclic networks: compatibility and enumeration

Graphs obtained from a binary leaf labeled ("phylogenetic") tree by adding an edge so as to introduce a cycle provide a useful representation of hybrid evolution in molecular evolutionary biology. This class of graphs (which we call "unicyclic networks") also has some attractive combinatorial properties, which we present. We characterize when a set of binary phylogenetic trees is displayed by a unicyclic network in terms of tree rearrangement operations. This leads to a triple-wise compatibility theorem and a simple, fast algorithm to determine 1-cycle compatibility. We also use generating function techniques to provide closed-form expressions that enumerate unicyclic networks with specified or unspecified cycle length, and we provide an extension to enumerate a class of multicyclic networks.     

Corollary discharge inhibition and audition in the stridulating cricket

The romantic notion of crickets singing on a warm summer’s evening is quickly dispelled when one comes ear to ear with a stridulating male. Remarkably, stridulating male crickets are able to hear sounds from the environment despite generating a 100 db song (Heiligenberg 1969; Jones and Dambach 1973). This review summarises recent work examining how they achieve this feat of sensory processing. While the responsiveness of the crickets’ peripheral auditory system (tympanic membrane, tympanic nerve, state of the acoustic spiracle) is maintained during sound production, central auditory neurons are inhibited by a feedforward corollary discharge signal precisely timed to coincide with the auditory neurons’ maximum response to self-generated sound. In this way, the corollary discharge inhibition prevents desensitisation of the crickets’ auditory pathway during sound production.     

Difficulties with Pitch Discrimination Influences Pitch Memory Performance: Evidence from Congenital Amusia

Music processing is influenced by pitch perception and memory. Additionally these features interact, with pitch memory performance decreasing as the perceived distance between two pitches decreases. This study examined whether or not the difficulty of pitch discrimination influences pitch retention by testing individuals with congenital amusia. Pitch discrimination difficulty was equated by determining an individual’s threshold with a two down one up staircase procedure and using this to create conditions where two pitches (the standard and the comparison tones) differed by 1x, 2x, and 3x the threshold setting. For comparison with the literature a condition that employed a constant pitch difference of four semitones was also included. The results showed that pitch memory performance improved as the discrimination between the standard and the comparison tones was made easier for both amusic and control groups, and more importantly, that amusics did not show any pitch retention deficits when the discrimination difficulty was equated. In contrast, consistent with previous literature, amusics performed worse than controls when the physical pitch distance was held constant at four semitones. This impaired performance has been interpreted as evidence for pitch memory impairment in the past. However, employing a constant pitch distance always makes the difference closer to the discrimination threshold for the amusic group than for the control group. Therefore, reduced performance in this condition may simply reflect differences in the perceptual difficulty of the discrimination. The findings indicate the importance of equating the discrimination difficulty when investigating memory.     

Variability in the role of the gasbladder in fish audition

The teleost gasbladder is believed to aid in fish audition by transferring pressure components of incoming sound to the inner ears. This idea is primarily based on both anatomical observations of the mechanical connection between the gasbladder and the ear, followed by physiological experiments by various researchers. The gasbladder movement has been modeled mathematically as a pulsating bubble. This study is extending the previous work on fish with a physical coupling of the gasbladder and ear by investigating hearing in two species (the blue gourami Trichogaster trichopterus, and the oyster toadfish Opsanus tau) without a mechanical linkage. An otophysan specialist (the goldfish Carassius auratus) with mechanical coupling, is used as the control. Audiograms were obtained with acoustically evoked potentials (e.g., auditory brainstem response) from intact fish and from the same individuals with their gasbladders deflated. In blue gourami and oyster toadfish, removal of gas did not significantly change thresholds, and evoked potentials had similar waveforms. In goldfish thresholds increased by 33–55 dB (frequency dependent) after deflation, and major changes in evoked potentials were observed. These results suggest that the gasbladder may not serve an auditory enhancement function in teleost fishes that lack mechanical coupling between the gasbladder and the inner ear. Accepted: 28 February 2000     

Indirect conductimetry: a novel approach to the conductimetric enumeration of microbial populations

A method is described for the indirect conductimetric assessment of microbial populations by the absorption of metabolic CO₂ in an alkaline absorbent solution whose conductance is monitored. The method allows microbial growth in un-modified conventional culture media to be monitored conductimetrically.     

Vowel Identity between Note Labels Confuses Pitch Identification in Non-Absolute Pitch Possessors

The simplest and likeliest assumption concerning the cognitive bases of absolute pitch (AP) is that at its origin there is a particularly skilled function which matches the height of the perceived pitch to the verbal label of the musical tone. Since there is no difference in sound frequency resolution between AP and non-AP (NAP) musicians, the hypothesis of the present study is that the failure of NAP musicians in pitch identification relies mainly in an inability to retrieve the correct verbal label to be assigned to the perceived musical note. The primary hypothesis is that, when asked to identify tones, NAP musicians confuse the verbal labels to be attached to the stimulus on the basis of their phonetic content. Data from two AP tests are reported, in which subjects had to respond in the presence or in the absence of visually presented verbal note labels (fixed Do solmization). Results show that NAP musicians confuse more frequently notes having a similar vowel in the note label. They tend to confuse e.g. a 261 Hz tone (Do) more often with Sol than, e.g., with La. As a second goal, we wondered whether this effect is lateralized, i.e. whether one hemisphere is more responsible than the other in the confusion of notes with similar labels. This question was addressed by observing pitch identification during dichotic listening. Results showed that there is a right hemispheric disadvantage, in NAP but not AP musicians, in the retrieval of the verbal label to be assigned to the perceived pitch. The present results indicate that absolute pitch has strong verbal bases, at least from a cognitive point of view.     

Catalase: its effect on microbial enumeration.

The addition of catalase to the surface of selective medium plates permitted increased enumeration of physically or chemically injured (stressed) microorganisms. Catalase acted by preventing the accumulation of hydrogen peroxide in, or around, injured cells. Heat-injured Staphylococcus aureus cells had decreased catalase activity, and heat-inactivated catalase had no effect on enumeration.     

The "Flash-Lag" effect occurs in audition and cross-modally

In 1958 MacKay showed that a rigidly moving object becomes visually fragmented when part of it is continuously visible but the rest is illuminated intermittently. For example, the glowing tip of a lit cigarette moving under stroboscopic illumination appeared to move ahead of the intermittently lit body. Latterly rediscovered as "the flash-lag effect" (FLE), this illusion now is typically demonstrated on a computer monitor showing two spots of light, one translating across the screen and another briefly flashed in vertical alignment with it. Despite being physically aligned, the brief flash is seen to lag behind the moving spot. This effect has recently motivated much fruitful research, prompting a variety of potential explanations, including those based on motion extrapolation, differential latency, attention, postdiction, and temporal integration (for review, see ). With no consensus on which theory is most plausible, we have broadened the scope of enquiry to include audition and have found that the FLE is not confined to vision. Whether the auditory motion stimulus is a frequency sweep or a translating sound source, briefly presented auditory stimuli lag behind auditory movement. In addition, when we used spatial motion, we found that the FLE can occur cross-modally. Together, these findings challenge several FLE theories and point to a discrepancy between internal brain timing and external stimulus timing.     

On the cyclic nature of perception in vision versus audition

Does our perceptual awareness consist of a continuous stream, or a discrete sequence of perceptual cycles, possibly associated with the rhythmic structure of brain activity? This has been a long-standing question in neuroscience. We review recent psychophysical and electrophysiological studies indicating that part of our visual awareness proceeds in approximately 7–13 Hz cycles rather than continuously. On the other hand, experimental attempts at applying similar tools to demonstrate the discreteness of auditory awareness have been largely unsuccessful. We argue and demonstrate experimentally that visual and auditory perception are not equally affected by temporal subsampling of their respective input streams: video sequences remain intelligible at sampling rates of two to three frames per second, whereas audio inputs lose their fine temporal structure, and thus all significance, below 20–30 samples per second. This does not mean, however, that our auditory perception must proceed continuously. Instead, we propose that audition could still involve perceptual cycles, but the periodic sampling should happen only after the stage of auditory feature extraction. In addition, although visual perceptual cycles can follow one another at a spontaneous pace largely independent of the visual input, auditory cycles may need to sample the input stream more flexibly, by adapting to the temporal structure of the auditory inputs.