Accumulating findings indicate that the beneficial effects of high-quality child care may be comparatively more pronounced for children from high-risk contexts. For instance, some work has shown that greater exposure to high-quality child care , or even simply attending regular non-maternal care , may mitigate the detrimental effects of economic adversity or low levels of maternal education on children’s subsequent academic achievement. Similar buffering effects have been noted with respect to children’s language development, such that exposure to high-quality language environments in child care may mitigate the negative effects of low-quality language environments experienced at home . Related findings also extend to children’s social development. For example, contrary to the replicated finding that more extensive hours in child care are predictive of heightened levels of aggression , increasing evidence suggests that the opposite may be true for children from high-risk home environments. Greater hours in high-quality child care have been linked with lower levels of internalizing and externalizing behavior in samples of low-income children . Similarly, using data from a large Canadian sample, Côté and colleagues found that the prototypically positive relation between non-maternal care and aggression in childhood was evident only for children from middle- to upper class families. Indeed, although it failed to reach statistical significance, blueberry packaging containers there was a descriptive indication that non-maternal care was associated with better socialoutcomes for low-income children.
We and our colleagues have recently shown similar findings with respect to child care exposure and several outcomes in pre-kindergarten . Specifically, we found that for children experiencing high levels of household chaos across early childhood, greater weekly hours in child care were predictive of comparatively fewer behavior problems. In particular, consistent with the idea of a buffering effect, greater child care exposure ameliorated the detrimental relation between household chaos and children’s social problems. We have also recently shown similar interactive relations with respect to children’s HPA axis functioning at 48 months of age ; specifically, using the same sample as in the present study, we found that the direction of the relation between child care exposure and children’s cortisol levels at 48 months varied as a function children’s broader environmental risk. For children from low-risk households, greater weekly hours of child care were predictive of higher cortisol levels. In contrast, for children facing substantial cumulative risks at home, greater hours of child care exposure were predictive of lower cortisol levels. Of note, and contrary to our hypotheses, is that other aspects of children’s experiences, such as caregiver responsivity and child care type, were unrelated to children’s cortisol level, irrespective of children’s home contexts. As such, the potential mechanisms underlying these relations remain unclear. Furthermore, this work was concerned with HPA axis functioning just prior to children’s transition to school in relation to their average child care experiences across early childhood.
Although this represents an important development span, we know little about the extent to which similar conditional relations are evident much earlier in development. Also, unlike the elegant within-person designs adopted by prior work that has considered links between child care and children’s diurnal rhythms on child care versus non–child care days, our findings comprised only between-child analyses. Most notably, they strengthen the internal validity of one’s inferences by essentially treating each individual as his or her own control group. In so doing, this holds all possible time-invariant confounds constant.The oscillation of the vocal folds is a primary characteristic of voice production. The oscillations extend primarily in the medio-lateral and vertical directions. During phonation, vocal fold movement is similar to a wave motion of the vocal fold surface starting inferiorly and continuing along the medial surface toward the superior surface of the vocal folds. In-vivo and ex-vivo analysis of the full larynx during phonation mainly permits observation, imaging, and quantification of the superior surface of the vocal folds and the vocal fold edges. Although such studies yield detailed quantitative information about vocal fold dynamics, several crucial aspects of vocal dynamics, such as mucosal wave propagation along the medial surface and the convergent divergent shape change of the glottal duct, can barely be captured from the top view. The hemilarynx methodology was developed to yield optical access to the entire surface dynamics of the vocal folds during phonation. It especially enables the visualization of the medial surface.
Experiments using the hemilarynx setup include ex-vivo human and animal models, in-vivo animal models, and in vitro synthetic models. In such setups, one vocal fold is removed and replaced by a glass plate or prism, yielding a direct view of the entire surface of the remaining vocal fold. Using an ex-vivo larynx setup, Jiang and Titze performed the first methodological study of the hemilarynx as a substitute for the full larynx. They demonstrated the validity of the results and also the potential to access the medial surface dynamics of the vocal fold. Later, Berry et al. quantitatively analyzed the dynamics of nine markers placed along one coronal cross-section of the medial surface of the vocal fold. In addition to the absolute displacement values, they performed a spatio-temporal analysis to calculate the empirical eigenfunctions of the reconstructed vocal fold dynamics. They showed that only two spatial eigenmodes were necessary to capture the major characteristics for periodic vocal fold oscillations. Moreover, the analysis of the eigenmodes suggested the physical mechanism of convergent-divergent shape changes of the glottal duct to facilitate the energy transfer from the airflow to the vocal fold tissues, which thus enabled sustained vocal fold oscillation.These initial studies utilized ex-vivo canine larynges, whereas subsequent investigations utilized ex-vivo human larynges. D€ollinger and Berry improved the ex-vivo hemilarynx methodology by mounting a grid of 30 sutures along the entire medial surface of the vocal fold. They also improved the calibration technique, yielding a decrease in the calibration error by more than two-thirds of the original value. Based on this improved setup, several studies were performed. The three dimensional motions of the entire vocal fold surface were visualized and quantified for normal vibrations. Mucosal wave propagation was reported for normal vocal fold dynamics. Spatio-temporal analysis confirmed theoretical assumptions regarding the convergent-divergent shape change of the glottal flow duct during normal vibration. It was found that the convergent-divergent glottal shape change is generated by the largest EEF , whereas the in-phase lateral movement of the vocal folds was captured within the second largest EEF . This again supported the basic physical mechanisms for sustained vocal fold oscillation. In addition to the basic investigations of normal phonation, the improved ex-vivo hemilarynx setup permits systematic variation of the elongation and adduction forces by pulling inferiorly at the thyroid cartilage and anteriorly at the muscular process of the arytenoid cartilage, respectively. First attempts were reported by D€ollinger and Berry. In studies with full larynx setups, blueberry packing boxes the adduction of the vocal folds showed a large influence on the quality of the voice signal. From an aerodynamic point of view, a high degree of adduction results in large glottal flow resistance which was demonstrated by Alipour and colleagues with ex-vivo full larynx models of different animal species.
That is, the higher the adduction, the higher is the force input or energy transfer into the vocal folds. In this context and in more general studies of the phonatory process, full synthetic and biological larynx models are used most commonly. However, except for numerical models, a supplementary investigation of the medial surface dynamics is nearly impossible. Therefore, in this work, we performed ex-vivo experiments with three human cadaver hemilarynges. In particular, we correlated vocal fold adduction with the glottal flow resistance and with the medial surface vocal fold dynamics. The goal of our study was to gain insights into the functional chain linking the subglottal pressure with the intraglottal aerodynamics and the resulting vocal fold dynamics, all as a function of glottal adduction. To achieve this goal, relations between glottal flow, subglottal pressure, and structural vocal fold dynamics were analyzed as a function of adduction. Our hypotheses are that: the vocal fold adduction is a key parameter for the control of the energy transfer from the airflow to the vocal folds; the dynamic shape characteristics of vocal fold oscillation determine the efficiency of the energy transfer; and EEF analysis allows the identification of specific characteristics of the vocal fold oscillations. As compared with previous work, the major innovative aspect of this study is the analysis and correlation of the aerodynamic influence of vocal fold adduction on the oscillatory behavior of the medial surface of the vocal folds, as identified and visualized through EEF analysis.To modify the degree of vocal fold adduction, a suture pierced the arytenoid cartilage at the MP to attach varying weights , Fig. 1. The purpose of this suture was designed to simulate the action of the lateral cricoarytenoid muscle. Another suture with a constant weight was attached anteriorly at the thyroid cartilage to provide slight longitudinal tension in the vocal fold to permit vibrations. The purpose of this suture was designed to simulate the action of the cricothyroid muscle. Self-sustained vibrations were induced by air pressure forces generated by a humidified and heated airflow, which passed through the trachea and through the hemiglottis. In this setup, the hemiglottis refers to the gap that is enclosed by the glass plate and the remaining vocal fold. Its oscillatory motion was recorded using a Photron Fastcam-Ultima APX high-speed digital camera ; settings are given in Table I. To track the movements of the medial surface of the vocal fold, 30 surgical microsutures were sewed into the mucosal epithelium, Fig. 2. The sutures were arranged in five vertical rows: r1 to r5 . Each vertical row consisted of six sutures: l1 to l6 , Fig. 2. The first four horizontal lines starting inferiorly were placed along the medial surface. The fifth horizontal line was placed close to the vocal fold edge; the sixth line was just above the vocal fold edge. The distance between two neighboring sutures was calculated as 1.96 6 0.3 mm. To avoid any disturbance of the natural dynamics of the vocal fold, an experienced phonosurgeon sewed the sutures to penetrate only the mucosal epithelium and not the superficial layer. Tracking of the sutures in the highspeed movies was performed semi-automatically on a subpixel basis. The user roughly marked the dark suture, which had dimensions of approximately 3 3 pixels and was easily detectable on the brighter tissue, by a mouse-click. Then the software calculated the center of mass of the dark pixels as the exact suture position. For calibration , a brass cube with edge length 5.0 mm was glued to the glass plate superior to the vocal fold, Fig. 2. On the other side of the glass plate, a right-angle prism was attached to yield two different visual perspectives of the medial surface of the vocal fold, simulating the recording situation with two cameras. Together with the calibration cube, this procedure permitted the reconstruction of the 3D coordinates of the mounted sutures. The computation of the physical coordinates of the sutures was performed using a previously described linear transformation method. For this method, a root mean-square linearization error can be computed to determine the accuracy of the experimental results. This lE error was determined as approximately 5%, which ensured sufficient accuracy. Pre-analysis: To examine whether the vocal fold actually adducted as adduction forces increased, the lateral coordinates of the two most posterior sutures close to the vocal fold edge r4l5 and r5l5 were computed after placing the weights. Lateral distances to the glass plate are given in Table II. The distances become smaller from MP10 to MP50 to MP100, indicating that the vocal folds move closer to the glass plate with increasing adduction forces. This confirms the correct function of the simulated adduction for all three larynges. Moreover, the decrease in distance as a percentage for MP50 and MP100 toward MP10 is given. It shows that for MP50, the effect is rather small and reaches 1%–21%. However, for MP100 the adduction effect is much more obvious and reduces the distances of the vocal fold to the glass plate to 6%–47%. Furthermore, the distances between vocal fold and glass plate are always smaller for MP100 than for MP50.