An optical/NIR survey of globular clusters in early-type galaxies III. On the colour bimodality of GC systems

The interpretation that bimodal colour distributions of globular clusters (GCs) reflect bimodal metallicity distributions has been challenged. Non-linearities in the colour to metallicity conversions caused by the horizontal branch (HB) stars may be responsible for transforming a unimodal metallicity distribution into a bimodal (optical) colour distribution. We study optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0 galaxies. We test whether the bimodal feature, generally present in optical colour distributions, remains in the optical/NIR ones. The latter colour combination is a better metallicity proxy than the former. We use KMM and GMM tests to quantify the probability that different colour distributions are better described by a bimodal, as opposed to a unimodal distribution. We find that double-peaked colour distributions are more commonly seen in optical than in optical/NIR colours. For some of the galaxies where the optical (g-z) distribution is clearly bimodal, the (g-K) and (z-K) distributions are better described by a unimodal distribution. The two most cluster-rich galaxies in our sample, NGC4486 and NGC4649, show some interesting differences. The (g-K) distribution of NGC4649 is better described by a bimodal distribution, while this is true for the (g-K) distribution of NGC4486 GCs only if restricted to a brighter sub-sample with small K-band errors (< 0.05 mag). Formally, the K-band photometric errors cannot be responsible for blurring bimodal metallicity distributions to unimodal (g-K) colour distributions. However, simulations including the extra scatter in the colour-colour diagrams (not fully accounted for in the photometric errors) show that such scatter may contribute to the disappearance of bimodality in (g-K) for the full NGC4486 sample. For the less cluster-rich galaxies results are inconclusive due to poorer statistics. [Abridged]Comment: A&A accepted, 15 pages, 10 figures, 4 table

Optimal integration of auditory and vibrotactile information for judgments of temporal order

Recent research that assessed spatial judgments about multisensory stimuli suggests that humans integrate multisensory inputs in a statistically optimal manner by weighting each input by its normalized reciprocal variance. Is integration similarly optimal When humans judge the temporal properties of bimodal stimuli? Twenty-four participants performed temporal order judgments (TOJs,) about 2 spatially separated stimuli. Stimuli were auditory, vibrotactile, or both. The temporal profiles of vibrotactile stimuli were manipulated to produce 3 levels of precision for TOJs. In bimodal conditions, the asynchrony between the 2 unimodal stimuli that comprised it bimodal Stimulus was manipulated to determine the weight given to touch. Bimodal performance on 2 measures-judgment uncertainty and tactile weight-was predicted With unimodal data. A model relying exclusively on audition wits rejected on the basis of both measures. A second model that selected the best input on each trial did not predict the reduced judgment uncertainty observed in bimodal trials. Only the optimal Maximum-likelihood-estimation model predicted both judgment uncertainties and weights the model's validity is extended to TOJs. Alternatives for modeling the process of event sequencing based on integrated multisensory inputs are discussed

Bimodal Infrared Colors of the M87 Globular Cluster System: Peaks in the Metallicity Distribution

The globular cluster (GC) systems of many galaxies reveal bimodal optical color distributions. Based on stellar evolutionary models and the bimodal colors and metallicities of Galactic GCs this is thought to reflect an underlying bimodal metallicity distribution. However, stars at many different phases of stellar evolution contribute to optical light. The I-H color is a much cleaner tracer of metallicity because it primarily samples the metallicity sensitive giant branch. Therefore, we use deep HST-NICMOS H, and WFPC2 optical observations, of M87 GCs to study their metallicity distribution. The M87 clusters are bimodal in I-H, for which there is no known physical explanation other than a bimodal metallicity distribution. Moreover, the two modes defined by the B-I and I-H colors are comprised of roughly the same two sets of objects, confirming that optical colors also primarily trace the metallicity. This is inconsistent with a recent suggestion based on one model of metallicity effects on the horizontal branch that bimodality arises from an underlying unimodal metallicity distribution due to a specific color-metallicity relation. We also find no discernable variation in the peak colors of the M87 GCs out to roughly 75 kpc due to the declining ratio of red-to-blue GCs, as implied by this model. Similarly, there is no evidence that the bimodal peaks are bluer for systems with large blue-to-red GC ratio. Our observations confirm that the primary cause of bimodality in cluster systems is an underlying bimodal metallicity distribution, and not the specific color-metallicity relationship defined by this horizontal branch model.Comment: Accepted for publication in ApJ Letters. 5 pages, 4 figs. Version 2 is identical to version

Mandarin speech perception in combined electric and acoustic stimulation.

For deaf individuals with residual low-frequency acoustic hearing, combined use of a cochlear implant (CI) and hearing aid (HA) typically provides better speech understanding than with either device alone. Because of coarse spectral resolution, CIs do not provide fundamental frequency (F0) information that contributes to understanding of tonal languages such as Mandarin Chinese. The HA can provide good representation of F0 and, depending on the range of aided acoustic hearing, first and second formant (F1 and F2) information. In this study, Mandarin tone, vowel, and consonant recognition in quiet and noise was measured in 12 adult Mandarin-speaking bimodal listeners with the CI-only and with the CI+HA. Tone recognition was significantly better with the CI+HA in noise, but not in quiet. Vowel recognition was significantly better with the CI+HA in quiet, but not in noise. There was no significant difference in consonant recognition between the CI-only and the CI+HA in quiet or in noise. There was a wide range in bimodal benefit, with improvements often greater than 20 percentage points in some tests and conditions. The bimodal benefit was compared to CI subjects' HA-aided pure-tone average (PTA) thresholds between 250 and 2000 Hz; subjects were divided into two groups: "better" PTA (&lt;50 dB HL) or "poorer" PTA (&gt;50 dB HL). The bimodal benefit differed significantly between groups only for consonant recognition. The bimodal benefit for tone recognition in quiet was significantly correlated with CI experience, suggesting that bimodal CI users learn to better combine low-frequency spectro-temporal information from acoustic hearing with temporal envelope information from electric hearing. Given the small number of subjects in this study (n = 12), further research with Chinese bimodal listeners may provide more information regarding the contribution of acoustic and electric hearing to tonal language perception