Figure 2

<p>Stimulus design and evoked potential responses. (a) Amplitude-time waveforms showing stimulus construction by adding band-passed, random phase noise (top, left) to repeating 3-note tone complexes (top, center) to produce the stimuli used in perceptual testing and for evoked-potential recording. There were five different tone complexes used; each is shown color-coded above its constituent components on an amplitude–frequency plot (bottom), where the components of each tone are overlaid on a common set of axes. (b,c) Amplitude spectra of the evoked potential responses from a single subject for two of the stimulus tones. The sum of the 0° and 180° responses is shown in black (envelope-related), and the difference of the 0° and 180° responses is shown in red or green (fine-structure phase-related). The y-axis is in units of relative amplitude; the corresponding measured values for the highest y-axis marker are 0.38 µV (black) and 0.35 µV (red) for Figure 2b, and 0.26 µV (black) and 0.23 µV (green) for Figure 2c. Colors refer to Figure 2a. (d,e) Mean relative amplitude spectra (n = 22 subjects) of peaks in the fine-structure-related (difference, Figure 2d) and envelope-related (sum, Figure 2e) evoked potential responses, all of which passed criteria for robustness (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000369#s4" target="_blank">Methods</a>). Responses to each stimulus tone have been overlaid on the same set of axes. Colors refer to Figure 2a. Error bars represent 95% confidence intervals around the mean value.</p

Pitch and Timbre Interfere When Both Are Parametrically Varied

<div><p>Pitch and timbre perception are both based on the frequency content of sound, but previous perceptual experiments have disagreed about whether these two dimensions are processed independently from each other. We tested the interaction of pitch and timbre variations using sequential comparisons of sound pairs. Listeners judged whether two sequential sounds were identical along the dimension of either pitch or timbre, while the perceptual distances along both dimensions were parametrically manipulated. Pitch and timbre variations perceptually interfered with each other and the degree of interference was modulated by the magnitude of changes along the un-attended dimension. These results show that pitch and timbre are not orthogonal to each other when both are assessed with parametrically controlled variations.</p></div

Mean hit rate and false alarm rates for all timbre and pitch distances in the two conditions.

<p>(SE in parentheses).</p

Lilliefors normality test p-values for the d’ scores in all conditions.

*<p>p-values <0.05 indicate a non-normal distribution.</p

No consistent directional effects of timbre on pure tone matching.

<p><b>Note:</b> The table shows uncorrected p-values for the slope of individual regression lines (matched tones regressed on timbre levels for each fundamental frequency f₀). p-values >0.05 mean that the hypothesis of equal slopes cannot be rejected. Uncorrected p-values are shown in this instance because these are the more conservative alternative when making the argument of no consistent directional effects. S1–10 indicates subjects from 1 to 10.</p>*<p>uncorrected p-value <0.05.</p>**<p>uncorrected p-value <0.01.</p

No consistent effect of timbre on the variability of pure tone matching.

<p><b>Note:</b> The table shows uncorrected p-values for the slopes of the individual regressions of the standard deviation of the matched tones on timbre levels for each fundamental frequency f₀. Uncorrected p-values are shown in this instance because these are the more conservative alternative when making the argument of no consistent directional effects. p-values >0.05 mean that the hypothesis of equal slopes cannot be rejected. S1–10 indicates subjects from 1 to 10.</p>*<p>uncorrected p-value <0.05.</p

Average sensitivity as a function of pitch and timbre variations.

<p>Values represent average d’ score (±SE) across subjects, for each intra-pair distance along the attended dimension (1step circle, 2 steps diamond or 3 steps triangle) and un-attended dimension (on the x-axis). (A) attend-timbre condition, n = 57 for each data point; (B) attend-pitch condition, n = 21 for each data point. ρ indicates the Spearman rank correlations coefficient between the d’ scores and the variations along the un-attended dimension, p indicates the p-values for the significance test.</p

Interspecies Avian Brain Chimeras Reveal That Large Brain Size Differences Are Influenced by Cell–Interdependent Processes

<div><p>Like humans, birds that exhibit vocal learning have relatively delayed telencephalon maturation, resulting in a disproportionately smaller brain prenatally but enlarged telencephalon in adulthood relative to vocal non-learning birds. To determine if this size difference results from evolutionary changes in cell-autonomous or cell-interdependent developmental processes, we transplanted telencephala from zebra finch donors (a vocal-learning species) into Japanese quail hosts (a vocal non-learning species) during the early neural tube stage (day 2 of incubation), and harvested the chimeras at later embryonic stages (between 9–12 days of incubation). The donor and host tissues fused well with each other, with known major fiber pathways connecting the zebra finch and quail parts of the brain. However, the overall sizes of chimeric finch telencephala were larger than non-transplanted finch telencephala at the same developmental stages, even though the proportional sizes of telencephalic subregions and fiber tracts were similar to normal finches. There were no significant changes in the size of chimeric quail host midbrains, even though they were innervated by the physically smaller zebra finch brain, including the smaller retinae of the finch eyes. Chimeric zebra finch telencephala had a decreased cell density relative to normal finches. However, cell nucleus size differences between each species were maintained as in normal birds. These results suggest that telencephalic size development is partially cell-interdependent, and that the mechanisms controlling the size of different brain regions may be functionally independent.</p> </div

Relative QN staining optical density in the subregions of the forebrains at ED9.

<p>QN optic densities in the subregions were normalized by the QN staining density in the tectum. QN optical density of the measured forebrain areas in quail embryos was higher than the optical density in chimera embryos (<i>p</i><0.001; nonparametric two way ANOVA; species×selected brain region). *: <i>p</i><0.004; t-test in the striatum, pallidum and hippocampus and Mann-Whitney rank sum test in the rest of the areas (n = 3 ZQ and 3 QU). Error bars S.E.M.</p

Proportions of telencephalon subregions in chimera at ED9 (A) and ED12 (B).

<p>There were no differences between groups; Kruskal–Wallis one-Way ANOVA, <i>p</i>>0.1 (at ED9, n = 4 ZF, 4 ZQ, and 3 QU; at ED12, n = 3 ZF, 3 ZQ, and 3 QU).</p