Two-point tactile discrimination ability is influenced by temporal features of stimulation

Two-point discrimination threshold is commonly used for assessing tactile spatial resolution. Since the effect of temporal features of cutaneous test stimulation on spatial discrimination ability is not yet well known, we determined whether the ability to discriminate between two stimulus locations varies with the interstimulus interval (ISI) of sequentially presented tactile stimuli or the length of the stimulus train. Electrotactile stimuli were applied to one or two locations on the skin of the thenar eminence of the hand in healthy human subjects. Tactile discrimination ability was determined using methods based on the signal detection theory allowing the assessment of sensory performance, independent of the subject’s response criterion. With stimulus pairs, the ability to discriminate spatial features of stimulation (one location vs. two stimulus locations 4 cm apart) was improved when the ISI was equal to or longer than that required for tactile temporal discrimination. With stimulus trains, the ability to discriminate spatial features of stimulation was significantly improved with an increase in the stimulus train (from 3 to 11 pulses corresponding to train lengths from 40 to 200 ms). These results indicate that temporal features of tactile stimulation significantly influence sensory performance in a tactile spatial discrimination task. Precise control of temporal stimulus parameters should help to reduce variations in results on the two-point discrimination threshold.     

Clinical spectrum and outcomes in families with coronal synostosis and TCF12 mutations

TCF12 mutations have been reported very recently in coronal synostosis. We report several cases of familial coronal synostosis among four families harbouring novel TCF12 mutations. We observed a broad interfamilial phenotypic spectrum with features overlapping with the Saethre–Chotzen syndrome. TCF12 molecular testing should be considered in patients with unilateral- or bilateral-coronal synostosis associated or not with syndactyly, after having excluded mutations in the TWIST1 gene and the p.Pro250Arg mutation in FGFR3.     

Delineation of EFTUD2 Haploinsufficiency‐Related Phenotypes Through a Series of 36 Patients

Mandibulofacial dysostosis, Guion‐Almeida type (MFDGA) is a recently delineated multiple congenital anomalies/mental retardation syndrome characterized by the association of mandibulofacial dysostosis (MFD) with external ear malformations, hearing loss, cleft palate, choanal atresia, microcephaly, intellectual disability, oesophageal atresia (OA), congenital heart defects (CHDs), and radial ray defects. MFDGA emerges as a clinically recognizable entity, long underdiagnosed due to highly variable presentations. The main differential diagnoses are CHARGE and Feingold syndromes, oculoauriculovertebral spectrum, and other MFDs. EFTUD2, located on 17q21.31, encodes a component of the major spliceosome and is disease causing in MFDGA, due to heterozygous loss‐of‐function (LoF) mutations. Here, we describe a series of 36 cases of MFDGA, including 24 previously unreported cases, and we review the literature in order to delineate the clinical spectrum ascribed to EFTUD2 LoF. MFD, external ear anomalies, and intellectual deficiency occur at a higher frequency than microcephaly. We characterize the evolution of the facial gestalt at different ages and describe novel renal and cerebral malformations. The most frequent extracranial malformation in this series is OA, followed by CHDs and skeletal abnormalities. MFDGA is probably more frequent than other syndromic MFDs such as Nager or Miller syndromes. Although the wide spectrum of malformations complicates diagnosis, characteristic facial features provide a useful handle.     

Overtone-based pitch selection in hermit thrush song: Unexpected convergence with scale construction in human music

Many human musical scales, including the diatonic major scale prevalent in Western music, are built partially or entirely from intervals (ratios between adjacent frequencies) corresponding to small-integer proportions drawn from the harmonic series. Scientists have long debated the extent to which principles of scale generation in human music are biologically or culturally determined. Data from animal “song” may provide new insights into this discussion. Here, by examining pitch relationships using both a simple linear regression model and a Bayesian generative model, we show that most songs of the hermit thrush (Catharus guttatus) favor simple frequency ratios derived from the harmonic (or overtone) series. Furthermore, we show that this frequency selection results not from physical constraints governing peripheral production mechanisms but from active selection at a central level. These data provide the most rigorous empirical evidence to date of a bird song that makes use of the same mathematical principles that underlie Western and many non-Western musical scales, demonstrating surprising convergence between human and animal “song cultures.” Although there is no evidence that the songs of most bird species follow the overtone series, our findings add to a small but growing body of research showing that a preference for small-integer frequency ratios is not unique to humans. These findings thus have important implications for current debates about the origins of human musical systems and may call for a reevaluation of existing theories of musical consonance based on specific human vocal characteristics.Many human musical scales, including the diatonic major scale prevalent in Western music, are built partially or entirely from intervals (ratios between adjacent frequencies) corresponding to small-integer ratios drawn from the harmonic series (1). A long-running debate concerns the extent to which principles underlying the structure of human musical scales derive from biological aspects of auditory perception and/or vocal production or are historical cultural “accidents” (2–4). The songs of nonhuman animals, such as birds or whales, potentially offer a valuable perspective on this debate. On the one hand, features of human music that are culturally bound, or dependent on specific characteristics of the human voice or auditory system, should be absent in animal vocalizations. On the other hand, aspects of human music observed in the vocalizations of other species seem likely to be partially determined by general physical or biological constraints rather than solely by cultural practices. Such shared features would complement recent research suggesting that common motor constraints shape both human song and that of some bird species (5).The physical principles underlying vocal production in songbirds are well understood (6–10) and do not differ fundamentally from those of other vertebrates. Sound is produced by tissue vibrations in the syrinx, a bird-specific organ located at the base of the trachea. Flow-driven vibrations of fleshy membranes within the syrinx (in songbirds, the medial and lateral labia) generate a periodic source signal that is filtered by the air column within the trachea and mouth and then emitted to the environment. These principles are important in formulating various alternative hypotheses considered below.Naturalists have long wondered whether birdsong could be said to have musical properties (11–13). However, early studies on pitch selection tended to be anecdotal, based on a small sample size, or lacking in analytical rigor. Two more recent studies specifically comparing pitch selection in bird song and human musical scales concluded that birdsong does not make preferential use of musical intervals found in commonly used Western musical scales (14, 15). However, because these studies each only examined one species [the white-throated sparrow (Zonotrichia albicollis) and the nightingale wren (Microcerculus philomela), respectively], a conclusion that birdsong in general does not exhibit musical properties seems premature. Indeed, other studies have shown preferential use of consonant intervals in tropical boubou shrikes (Laniarius aethiopicus) (16) and musician wrens (Cyphorhinus arada) (17), although in the first case no rigorous statistical analysis was presented.Here, we investigated songs of the hermit thrush (Catharus guttatus), a medium-sized North American songbird whose famously “musical”-sounding song has attracted the attention of ornithologists and musicians alike (18) but has not yet been subjected to detailed pitch analysis. Its songs are composed of elements (the smallest unit of song construction, seen as continuous uninterrupted traces on spectrograms) that may exhibit either a variable pitch, such as trills and slides, or a stable pitch—pure, non-frequency-modulated, “flutelike” sounds. These stable sounds, which we refer to as “notes” (Fig. 1), are characterized by strong fundamental frequencies and very weak higher harmonics, making them ideally suited for an analysis of pitch relationships (15). Males typically sing 6–10 different song types, defined as nearly identical sequences of elements, durations, and frequencies. In a number of early- and mid-20th-century studies, hermit thrush song was variously attributed with use of major, minor, and pentatonic scales (19, 20) and claimed to follow the overtone series (21). However, these early studies again suffered from small sample sizes and anecdotal reporting and were not based on rigorous acoustic analysis. More recent hermit thrush studies have focused on regional differences and song-type ordering, rather than pitch selection (22, 23).Open in a separate windowFig. 1.Song of the hermit thrush (C. guttatus). One song type of a single male hermit thrush, illustrating the various elements that can be observed in songs of this species. Only “notes” (elements with stable pitch) were analyzed in this study because the other element types have no clearly defined or measurable pitch.Here we tested the overtone hypothesis, which predicts that the frequencies of the individual song notes are integer multiples (harmonics) of an implied (but not actually sung) base frequency (hereafter f_i). This hypothesis seems plausible because, unlike some previous claims, it does not attribute human-specific music-theoretical concepts to hermit thrush song. Moreover, the subjective impression of trained musicians listening to hermit thrush songs (played at one-sixth of the original speed to shift the speed and frequency of the songs into a range more suitable for human hearing) was that most notes indeed seemed to follow an overtone series (see Fig. 2 and Audio File S1 for the corresponding sound example). However, determining whether a set of notes are harmonics of a frequency not present in the set requires a rigorous procedure to estimate and evaluate f_i. To this end, we used two different statistical approaches, an ordinary least-squares regression model and a generative Bayesian estimator. Both approaches were used to test the hypothesis that a song is an exchangeable sequence of frequencies that are integer multiples of some implied f_i, versus the null hypothesis that songs are generated by drawing frequencies out of a random log-normal distribution (see Materials and Methods for details). By using a Bayesian approach in addition to the least-squares regression model we evaluate whether our analyses represent a rigorous test of our overtone hypothesis and not simply a post hoc explanation that minimizes an error measure by “memorizing” the data. These properties make the Bayesian evaluation statistically more rigorous than least-squares fitting.Open in a separate windowFig. 2.Frequency distribution of a hermit thrush song compared with an overtone series. (A) Notes of a hermit thrush song. (B) The same notes rearranged in ascending order to show how they correspond to overtones 3, 4, 5, and 6 of an overtone series fitted to the frequencies corresponding to these notes (the complete stacked overtone series is shown on the right).