Publications by authors named "Adrian M Bartlett"

2 Publications

  • Page 1 of 1

Speech-like rhythm in a voiced and voiceless orangutan call.

PLoS One 2015 8;10(1):e116136. Epub 2015 Jan 8.

Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, the Netherlands.

The evolutionary origins of speech remain obscure. Recently, it was proposed that speech derived from monkey facial signals which exhibit a speech-like rhythm of ∼5 open-close lip cycles per second. In monkeys, these signals may also be vocalized, offering a plausible evolutionary stepping stone towards speech. Three essential predictions remain, however, to be tested to assess this hypothesis' validity; (i) Great apes, our closest relatives, should likewise produce 5Hz-rhythm signals, (ii) speech-like rhythm should involve calls articulatorily similar to consonants and vowels given that speech rhythm is the direct product of stringing together these two basic elements, and (iii) speech-like rhythm should be experience-based. Via cinematic analyses we demonstrate that an ex-entertainment orangutan produces two calls at a speech-like rhythm, coined "clicks" and "faux-speech." Like voiceless consonants, clicks required no vocal fold action, but did involve independent manoeuvring over lips and tongue. In parallel to vowels, faux-speech showed harmonic and formant modulations, implying vocal fold and supralaryngeal action. This rhythm was several times faster than orangutan chewing rates, as observed in monkeys and humans. Critically, this rhythm was seven-fold faster, and contextually distinct, than any other known rhythmic calls described to date in the largest database of the orangutan repertoire ever assembled. The first two predictions advanced by this study are validated and, based on parsimony and exclusion of potential alternative explanations, initial support is given to the third prediction. Irrespectively of the putative origins of these calls and underlying mechanisms, our findings demonstrate irrevocably that great apes are not respiratorily, articulatorilly, or neurologically constrained for the production of consonant- and vowel-like calls at speech rhythm. Orangutan clicks and faux-speech confirm the importance of rhythmic speech antecedents within the primate lineage, and highlight potential articulatory homologies between great ape calls and human consonants and vowels.
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January 2016

Saccades during object viewing modulate oscillatory phase in the superior temporal sulcus.

J Neurosci 2011 Dec;31(50):18423-32

Neuroscience Graduate Diploma Program, Department of Psychology, Centre for Vision Research, York University, Toronto, Ontario M3J 1P3, Canada.

Saccadic eye movements (SEMs) are the primary means of gating visual information in primates and strongly influence visual perception. The active exploration of the visual environment ("active vision") via SEMs produces suppression during saccades and enhancement afterward (i.e., during fixation) in occipital visual areas. In lateral temporal lobe visual areas, the influence, if any, of eye movements is less well understood, despite the necessity of these areas for forming coherent percepts of objects. The upper bank of the superior temporal sulcus (uSTS) is one such area whose sensitivity to SEMs is unknown. We therefore examined how saccades modulate local field potentials (LFPs) in the uSTS of macaque monkeys while they viewed face and nonface object stimuli. LFP phase concentration increased following fixation onset in the alpha (8-14 Hz), beta (14-30 Hz), and gamma (30-60 Hz) bands and was distinct from the image-evoked response. Furthermore, near-coincident onsets of fixation and image presentation--like those occurring in active vision--led to enhanced responses through greater phase concentration in the same frequency bands. Finally, single-unit activity was modulated by the phase of alpha, beta, and gamma oscillations, suggesting that the observed phase-locking influences spike timing in uSTS. Previous research implicates phase concentration in these frequency bands as a correlate of perceptual performance (Womelsdorf et al., 2006; Bosman et al., 2009). Together, these results demonstrate sensitivity to eye movements in an object-processing region of the brain and represent a plausible neural basis for the enhancement of object processing during active vision.
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Source Listing
December 2011