Elite Scientists and the Global Brain Drain

There are signs – one is world university league tables – that people increasingly think globally when choosing the university in which they wish to work and study. This paper is an exploration of data on the international brain drain. We study highly-cited physicists, highly-cited bio-scientists, and assistant professors of economics. First, we demonstrate that talented researchers are being systematically funnelled into a small number of countries. Among young economists in the top American universities, for example, 75% did their undergraduate degree outside the United States. Second, the extent of the elite brain drain is considerable. Among the world’s top physicists, nearly half no longer work in the country in which they were born. Third, the USA and Switzerland are per capita the largest net-importers of elite scientists. Fourth, we estimate the migration ‘funnelling coefficient’ at approximately 0.2 (meaning that 20% of top researchers tend to leave their country at each professional stage). Fifth, and against our prior expectations, the productivity of top scientists, as measured by the Hirsch h-index, is similar between the elite movers and stayers. Thus it is apparently not true that it is disproportionately the very best people who emigrate. Sixth, there is extreme clustering of ISI Highly Cited Researchers into particular fields in different universities. Seventh, we debate the questions: are the brain drain and this kind of funnelling good or bad for the world, and how should universities and governments respond?

Speech intelligibility prediction in reverberation: Towards an integrated model of speech transmission, spatial unmasking, and binaural de-reverberation

Room acoustic indicators of intelligibility have focused on the effects of temporal smearing of speech by reverberation and masking by diffuse ambient noise. In the presence of a discrete noise source, these indicators neglect the binaural listener's ability to separate target speech from noise. Lavandier and Culling [(2010). J. Acoust. Soc. Am. 127, 387–399] proposed a model that incorporates this ability but neglects the temporal smearing of speech, so that predictions hold for near-field targets. An extended model based on useful-to-detrimental (U/D) ratios is presented here that accounts for temporal smearing, spatial unmasking, and binaural de-reverberation in reverberant environments. The influence of the model parameters was tested by comparing the model predictions with speech reception thresholds measured in three experiments from the literature. Accurate predictions were obtained by adjusting the parameters to each room. Room-independent parameters did not lead to similar performances, suggesting that a single U/D model cannot be generalized to any room. Despite this limitation, the model framework allows to propose a unified interpretation of spatial unmasking, temporal smearing, and binaural de-reverberation. I. INTROD

Auditory compensation for head rotation is incomplete

Hearing is confronted by a similar problem to vision when the observer moves. The image motion that is created remains ambiguous until the observer knows the velocity of eye and/or head. One way the visual system solves this problem is to use motor commands, proprioception and vestibular information. These ‘extra-retinal signals’ compensate for self movement, converting image motion into head-centred coordinates, though not always perfectly. We investigated whether the auditory system also transforms coordinates by examining the degree of compensation for head rotation when judging a moving sound. Real-time recordings of head motion were used to change the ‘movement gain’ relating head movement to source movement across a loudspeaker array. We then determined psychophysically the gain that corresponded to a perceptually-stationary source. Experiment 1 showed that the gain was small and positive for a wide range of trained head speeds. Hence listeners perceived a stationary source as moving slightly opposite to the head rotation, in much the same way that observers see stationary visual objects move against a smooth pursuit eye movement. Experiment 2 showed the degree of compensation remained the same for sounds presented at different azimuths, although the precision of performance declined when the sound was eccentric. We discuss two possible explanations for incomplete compensation, one based on differences in the accuracy of signals encoding image motion and self-movement, and one concerning statistical optimisation that sacrifices accuracy for precision. We then consider the degree to which such explanations can be applied to auditory motion perception in moving listeners

Reverberation limits the release from informational masking obtained in the harmonic and binaural domains

A difference in fundamental frequency (ΔF0) and a difference in spatial location (ΔSL) are two cues known to provide masking releases when multiple speakers talk at once in a room. Situations were examined in which reverberation should have no effect on the mechanisms underlying the release from energetic masking produced by these two cues. Speech reception thresholds using both unpredictable target sentences and the coordinate response measure followed a similar pattern. Both ΔF0s and ΔSLs provided masking releases in the presence of non-speech maskers (matched in excitation pattern and temporal envelope to speech maskers) which, as intended, were robust to reverberation. Larger masking releases were obtained for speech maskers, but critically, they were affected by reverberation. The results suggest that reverberation either limits the amount of informational masking there is to begin with, or affects its release by ΔF0s or ΔSLs

Cochlear implant simulator with independent representation of the full spiral ganglion

In cochlear implant simulation with vocoders, narrow-band carriers deliver the envelopes from each analysis band to the cochlear positions of the simulated electrodes. However, this approach does not faithfully represent the continuous nature of the spiral ganglion. The proposed “SPIRAL” vocoder simulates current spread by mixing all envelopes across many tonal carriers. SPIRAL demonstrated that the classic finding of reduced speech-intelligibility benefit with additional electrodes could be due to current spread. SPIRAL produced lower speech reception thresholds than an equivalent noise vocoder. These thresholds are stable for between 20 and 160 carriers

Measurements of inter-cochlear level and phase differences of bone-conducted sound

Bone-anchored hearing aids are a widely used method of treating conductive hearing loss, but the benefit of bilateral implantation is limited due to interaural cross-talk. The present study measured the phase and level of pure tones reaching each cochlea from a single, mastoid placed bone transducer on normal hearing participants. In principle, the technique could be used to implement a cross-talk cancellation system in those with bilateral bone conductors. The phase and level of probe tones over two insert earphones was adjusted until they canceled sound from a bone transducer (i.e., resulting in perceived silence). Testing was performed in 50-Hz steps between 0.25 and 8 kHz. Probe phase and level results were used to calculate inter-cochlear level and phase differences. The inter-cochlear phase differences of the bone-conducted sound were similar for all three participants showing a relatively linear increase between 4 and 8 kHz. The attenuation characteristics were highly variable over the frequency range as well as between participants. This variability was thought to be related to differences in skull dynamics across the ears. Repeated measurements of cancellation phase and level of the same frequency produced good consistency across sessions from the same participant