Forward shift of feeding buzz components of dolphins and belugas during associative learning reveals a likely connection to reward expectation, pleasure and brain dopamine activation.

For many years, we heard sounds associated with reward from dolphins and belugas. We named these pulsed sounds victory squeals (VS), as they remind us of a child's squeal of delight. Here we put these sounds in context with natural and learned behavior. Like bats, echolocating cetaceans produce feeding buzzes as they approach and catch prey. Unlike bats, cetaceans continue their feeding buzzes after prey capture and the after portion is what we call the VS. Prior to training (or conditioning), the VS comes after the fish reward; with repeated trials it moves to before the reward. During training, we use a whistle or other sound to signal a correct response by the animal. This sound signal, named a secondary reinforcer (SR), leads to the primary reinforcer, fish. Trainers usually name their whistle or other SR a bridge, as it bridges the time gap between the correct response and reward delivery. During learning, the SR becomes associated with reward and the VS comes after the SR rather than after the fish. By following the SR, the VS confirms that the animal expects a reward. Results of early brain stimulation work suggest to us that SR stimulates brain dopamine release, which leads to the VS. Although there are no direct studies of dopamine release in cetaceans, we found that the timing of our VS is consistent with a response after dopamine release. We compared trained vocal responses to auditory stimuli with VS responses to SR sounds. Auditory stimuli that did not signal reward resulted in faster responses by a mean of 151 ms for dolphins and 250 ms for belugas. In laboratory animals, there is a 100 to 200 ms delay for dopamine release. VS delay in our animals is similar and consistent with vocalization after dopamine release. Our novel observation suggests that the dopamine reward system is active in cetacean brains.

Vocal reporting of echolocation targets: dolphins often report before click trains end.

Bottlenose dolphins (Tursiops truncatus) wore opaque suction cups over their eyes while stationing behind an acoustically opaque door. This put the dolphins in a known position and orientation. When the door opened, the dolphin clicked to detect targets. Trainers specified that Dolphin S emit a whistle if the target was a 7.5 cm water filled sphere, or a pulse burst if the target was a rock. S remained quiet if there was no target. Dolphin B whistled for the sphere. She remained quiet for rock and for no target. Thus, S had to choose between three different responses, whistle, pulse burst, or remain quiet. B had to choose between two different responses, whistle or remain quiet. S gave correct vocal responses averaging 114 ms after her last echolocation click (range 182 ms before and 219 ms after the last click). Average response for B was 21 ms before her last echolocation click (range 250 ms before and 95 ms after the last click in the train). More often than not, B began her whistle response before her echolocation train ended. The findings suggest separate neural pathways for generation of response vocalizations as opposed to echolocation clicks.

Modulation of field emission properties of znO nanorods during arc discharge.

Zinc oxide (ZnO) nanorods have been synthesized via the arc discharge method. Different oxygen partial pressures were applied in the arc discharge chamber to modulate the field emission properties of the as-synthesized ZnO nanorods. Scanning electron microscopy (SEM) was carried out to analyze the morphology of the ZnO nanorods. The ion beam analysis technique of proton induced X-ray emission (PIXE) was performed to probe the impurities in ZnO nanorods. SEM images clearly revealed the formation of randomly oriented ZnO nanorods with diameters between 10-50 nm. It was found that the morphology and the electrical properties of the ZnO nanorods were dependent on the oxygen partial pressure during arc discharge. In addition enhanced UV-sensitive photoconductivity was found for ZnO nanorods synthesized at high oxygen partial pressure during arc discharge. The field emission properties of the nanorods were studied. The turn-on field, which is defined at a current density of 10 microA cm(-2), was about 3 V microm(-1) for ZnO nanorods synthesized at 99% oxygen partial pressure during arc discharge. The turn-on field for ZnO nanorods increased with the decrease of oxygen partial pressure during arc discharge. The simplicity of the synthesis route coupled with the modulation of field emission properties due to the arc discharge method make the ZnO nanorods a promising candidate for a low cost and compact cold cathode material.

Electron beam annealing of Fe+ implanted Si nanostructures.

Silicon nanostructures (nanowhiskers) have been formed at surface densities approximately 10(9) cm-2 by electron beam annealing (EBA) prior to the implantation of 7 keV Fe+ ions to fluences from 1 x 10(13) - 4 x 10(15) Fe+ cm(-2). A second EBA step is then applied to relieve implantation-induced stresses. RBS analysis shows that the implanted Fe remains close to the surface. AFM characterisations of the implanted nanowhiskers before and after the final EBA step are summarised in graphs of height versus surface density. In a striking result it is shown that the nanowhiskers not only survive processing but also grow significantly. For example, at the highest fluence of 4 x 10(15) Fe+ cm(-2), the average height more than doubles: the increases are from 5.0 nm to 6.5 nm under implantation and from 6.5 nm to 11.8 nm under EBA. In addition there is a significant increase in surface density from an initial value of 1.6 x 10(9) cm(-2) to 4.3 x 10(9) cm(-2). These results highlight the feasibility of doping Si surface nanostructures with magnetic ions to fabricate Si devices for spin-dependent enhanced field emission.

Stimulated terahertz stokes emission of silicon crystals doped with antimony donors.

Stimulated Stokes emission has been observed from silicon crystals doped by antimony donors when optically excited by radiation from a tunable infrared free electron laser. The photon energy of the emission is equal to the pump photon energy reduced by the energy of the intervalley transverse acoustic (TA) g phonon in silicon (approximately 2.92 THz). The emission frequency covers the range of 4.6-5.8 THz. The laser process occurs due to a resonant coupling of the 1s(E) and 1s(A1) donor states (separation approximately 2.97 THz) via the g-TA phonon, which conserves momentum and energy within a single impurity center.

Hearing and whistling in the deep sea: depth influences whistle spectra but does not attenuate hearing by white whales (Delphinapterus leucas) (Odontoceti, Cetacea).

Hearing is attenuated in the aerial ear of humans and other land mammals tested in pressure chambers as a result of middle ear impedance changes that result from increased air density. We tested the hypothesis, based on recent middle ear models, that increasing the density of middle ear air at depth might attenuate whale hearing. Two white whales Delphinapterus leucas made dives to a platform at a depth of 5, 100, 200 or 300 m in the Pacific Ocean. During dives to station on the platform for up to 12 min, the whales whistled in response to 500 ms tones projected at random intervals to assess their hearing threshold at each depth. Analysis of response whistle spectra, whistle latency in response to tones and hearing thresholds showed that the increased hydrostatic pressure at depth changed each whale's whistle response at depth, but did not attenuate hearing overall. The finding that whale hearing is not attenuated at depth suggests that sound is conducted through the head tissues of the whale to the ear without requiring the usual ear drum/ossicular chain amplification of the aerial middle ear. These first ever hearing tests in the open ocean demonstrate that zones of audibility for human-made sounds are just as great throughout the depths to which these whales dive, or at least down to 300 m.

Auditory and behavioral responses of bottlenose dolphins (Tursiops truncatus) and a beluga whale (Delphinapterus leucas) to impulsive sounds resembling distant signatures of underwater explosions.

A behavioral response paradigm was used to measure masked underwater hearing thresholds in two bottlenose dolphins and one beluga whale before and after exposure to impulsive underwater sounds with waveforms resembling distant signatures of underwater explosions. An array of piezoelectric transducers was used to generate impulsive sounds with waveforms approximating those predicted from 5 or 500 kg HBX-1 charges at ranges from 1.5 to 55.6 km. At the conclusion of the study, no temporary shifts in masked-hearing thresholds (MTTSs), defined as a 6-dB or larger increase in threshold over pre-exposure levels, had been observed at the highest impulse level generated (500 kg at 1.7 km, peak pressure 70 kPa); however, disruptions of the animals' trained behaviors began to occur at exposures corresponding to 5 kg at 9.3 km and 5 kg at 1.5 km for the dolphins and 500 kg at 1.9 km for the beluga whale. These data are the first direct information regarding the effects of distant underwater explosion signatures on the hearing abilities of odontocetes.

Temporary shift in masked hearing thresholds of bottlenose dolphins, Tursiops truncatus, and white whales, Delphinapterus leucas, after exposure to intense tones.

A behavioral response paradigm was used to measure masked underwater hearing thresholds in five bottlenose dolphins and two white whales before and immediately after exposure to intense 1-s tones at 0.4, 3, 10, 20, and 75 kHz. The resulting levels of fatiguing stimuli necessary to induce 6 dB or larger masked temporary threshold shifts (MTTSs) were generally between 192 and 201 dB re: 1 microPa. The exceptions occurred at 75 kHz, where one dolphin exhibited an MTTS after exposure at 182 dB re: 1 microPa and the other dolphin did not show any shift after exposure to maximum levels of 193 dB re: 1 microPa, and at 0.4 kHz, where no subjects exhibited shifts at levels up to 193 dB re: 1 microPa. The shifts occurred most often at frequencies above the fatiguing stimulus. Dolphins began to exhibit altered behavior at levels of 178-193 dB re: 1 microPa and above; white whales displayed altered behavior at 180-196 dB re: 1 microPa and above. At the conclusion of the study all thresholds were at baseline values. These data confirm that cetaceans are susceptible to temporary threshold shifts (TTS) and that small levels of TTS may be fully recovered.

Hearing deficits measured in some Tursiops truncatus, and discovery of a deaf/mute dolphin.

Eight bottlenose dolphins Tursiops truncatus (four male, four female) were trained to respond to 100-ms tones. Three male dolphins (ages 23, 26, and 34) exhibited hearing disability at four higher frequencies-70, 80, 100, and 120 kHz even at 111-135 dB re: 1 microPa. Two females (ages 32 and 35) responded to all frequencies as did a male (age 7) and a female (age 11). One female (age 33) responded to all tones at 80 kHz and below; however, she failed to respond at 100 or 120 kHz. One young female dolphin (age 9) exhibited no perception of sound to behavioral or electrophysiological tests. This young female was not only deaf, but mute. The dolphin was monitored periodically by hydrophone and daily by trainers (by ear in air) for 7 years until she was age 16. The animal never whistled or made echolocation pulses or made burst pulse sounds as other dolphins do.

Demonstration of adaptation in beluga whale echolocation signals.

The echolocation signals of the same beluga whale (Delphinapterus leucas) were measured first in San Diego Bay, and later in Kaneohe Bay, Oahu, Hawaii. The ambient noise level in Kaneohe Bay is typically 12-17 dB greater than in San Diego Bay. The whale demonstrated the adaptiveness of its biosonar by shifting to higher frequencies and intensities after it was moved to Kaneohe. In San Diego, the animal emitted echolocation signals with peak frequencies between 40 and 60 kHz, and bandwidths between 15 and 25 kHz. In Kaneohe, the whale shifted its signals approximately an octave higher in frequencies with peak frequencies between 100 and 120 kHz, and bandwidths between 20 and 40 kHz. Signal intensities measured in Kaneohe were up to 18 dB higher than in San Diego. The data collected represent the first quantitative evidence of the adaptive capability of a cetacean biosonar system.

Auditory brainstem response in dolphins.

We recorded the auditory brainstem response (ABR) in four dolphins (Tursiops truncatus and Delphinus delphis). The ABR evoked by clicks consists of seven waves within 10 msec; two waves often contain dual peaks. The main waves can be identified with those of humans and laboratory mammals; in spite of a much longer path, the latencies of the peaks are almost identical to those of the rat. The dolphin ABR waves increase in latency as the intensity of a sound decreases by only 4 microseconds/decibel(dB) (for clicks with peak power at 66 kHz) compared to 40 microseconds/dB in humans (for clicks in the sonic range). Low-frequency clicks (6-kHz peak power) show a latency increase about 3 times (12 microseconds/dB) as great. Although the dolphin brainstem tracks individual clicks to at least 600 per sec, the latency increases and amplitude decreases with increasing click rates. This effect varies among different waves of the ABR; it is around one-fifth the effect seen in man. The dolphin brain is specialized for handling brief, frequent clicks. A small latency difference is seen between clicks 180 degrees different in phase--i.e., with initial compression vs. initial rarefaction. The ABR can be used to test theories of dolphin sonar signal processing. Hearing thresholds can be evaluated rapidly. Cetaceans that have not been investigated can now be examined, including the great whales, a group for which data are now completely lacking.