Hypothesis Claims Research Articles

Common species have lower taxonomic diversity Evidence from the urban floras of Brussels and Rome

ABSTRACTThe species pool hypothesis claims that the large‐scale regional species pool is the chief parameter in determining small‐scale species richness through filtering of species that can persist within a community on the basis of their tolerance of the abiotic environment. Accordingly, different environmental conditions give rise to different species assemblages. From a taxonomic perspective, under the assumption of trait conservatism, co‐occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. The next step consists in understanding how commonness and rarity of individual species produce the observed taxonomic diversity. In this paper, the importance of environmental filtering in regulating the taxonomic structure of rare and common plant species in the urban floras of Brussels (Belgium) and Rome (Italy) is tested. First, we computed the taxonomic diversity of the rare and common species of Brussels and Rome based on the branching topology of the Linnaean taxonomic trees. Next, using a randomization procedure, we determined whether the taxonomic diversity of the rare species was significantly higher than the diversity of the common species. Results show that, for both urban floras, common species that shape the community matrix and experience similar environmental conditions have a taxonomic diversity that is significantly lower than that of the rare species that represent a relatively incidental set of species of more ‘disperse’ origin. Finally, from a conservation/management perspective our results imply that, given their high taxonomic heterogeneity, the protection of rare species is a central issue for preserving high levels of diversity in urban areas.

Discourse structure and relative clause processing

Studies in several languages have shown that subject-relative clauses are easier to process than object-relative clauses. Mak, Vonk, and Schriefers (2006) have proposed the topichood hypothesis to account for the preference for subject-relative clauses. This hypothesis claims that the entity in the relative clause that is most topicworthy will be chosen as the subject. By default, the antecedent of the relative clause will be chosen as the subject of the relative clause, because it is the topic of the relative clause. However, when the noun phrase (NP) in the relative clause is also topicworthy, the preference for the antecedent to be the subject will disappear. This was confirmed in two experiments. In Experiment 1, we tested relative clauses with a personal pronoun in the relative clause. We obtained a preference for object-relative clauses, in line with the assumption that personal pronouns refer to a discourse topic and are thus topicworthy. In Experiment 2, the discourse status of the NP in the relative clause was manipulated; either it was not present in the preceding context, or it was the discourse topic. The experiment showed that when the NP in the relative clause refers to the discourse topic, the difficulty of object-relative clauses is reduced, in comparison with relative clauses with an NP that is new in the discourse, even in the absence of any explicit cue in the relative clause itself. The experiments show that discourse factors guide processing at the sentence level.

Reading Ability: Lexical Quality to Comprehension

The lexical quality hypothesis (LQH) claims that variation in the quality of word representations has consequences for reading skill, including comprehension. High lexical quality includes well-specified and partly redundant representations of form (orthography and phonology) and flexible representations of meaning, allowing for rapid and reliable meaning retrieval. Low-quality representations lead to specific word-related problems in comprehension. Six lines of research on adult readers demonstrate some of the implications of the LQH. First, large-scale correlational results show the general interdependence of comprehension and lexical skill while identifying disassociations that allow focus on comprehension-specific skill. Second, word-level semantic processing studies show comprehension skill differences in the time course of form-meaning confusions. Studies of rare vocabulary learning using event-related potentials (ERPs) show that, third, skilled comprehenders learn new words more effectively and show stronger ERP indicators for memory of the word learning event and, fourth, suggest skill differences in the stability of orthographic representations. Fifth, ERP markers show comprehension skill differences in meaning processing of ordinary words. Finally, in text reading, ERP results demonstrate momentary difficulties for low-skill comprehenders in integrating a word with the prior text. The studies provide evidence that word-level knowledge has consequences for word meaning processes in comprehension.

The Role of Market Forces and Legal Institutions in Bonding Cross-Listed Firms

The bonding hypothesis claims that firms can cross list in countries with strong institutions to assure shareholders that managers will not expropriate resources from the firm. However, current research does not examine whether legal institutions and/or market forces lead to this bonding effect. To shed light on the mechanisms that allow firms to bond, I examine the association between country-level institutions and the change in analyst coverage around cross listings. I document that analyst coverage increases after a cross listing in a variety of different host markets, but the increase is highest for firms that list in host markets with strong market forces or strong legal institutions. This suggests that, in addition to traditional legal institutions, market forces can also play a role in bonding cross listed firms.

On‐line processing of wh‐questions in children with G‐SLI and typically developing children

The computational grammatical complexity (CGC) hypothesis claims that children with G(rammatical)-specific language impairment (SLI) have a domain-specific deficit in the computational system affecting syntactic dependencies involving 'movement'. One type of such syntactic dependencies is filler-gap dependencies. In contrast, the Generalized Slowing Hypothesis claims that SLI children have a domain-general deficit affecting processing speed and capacity. To test contrasting accounts of SLI we investigate processing of syntactic (filler-gap) dependencies in wh-questions. Fourteen 10;2-17;2 G-SLI children, 14 age-matched and 17 vocabulary-matched controls were studied using the cross-modal picture-priming paradigm. G-SLI children's processing speed was significantly slower than the age controls, but not younger vocabulary controls. The G-SLI children and vocabulary controls did not differ on memory span. However, the typically developing and G-SLI children showed a qualitatively different processing pattern. The age and vocabulary controls showed priming at the gap, indicating that they process wh-questions through syntactic filler-gap dependencies. In contrast, G-SLI children showed priming only at the verb. The findings indicate that G-SLI children fail to establish reliably a syntactic filler-gap dependency and instead interpret wh-questions via lexical-thematic information. These data challenge the Generalized Slowing Hypothesis account, but support the CGC hypothesis, according to which G-SLI children have a particular deficit in the computational system affecting syntactic dependencies involving 'movement'. As effective remediation often depends on aetiological insight, the discovery of the nature of the syntactic deficit, along side a possible compensatory use of semantics to facilitate sentence processing, can be used to direct therapy. However, the therapeutic strategy to be used, and whether such similar strengths and weaknesses within the language system are found in other SLI subgroups are empirical issues that warrant further research.

The effects of prohibiting gestures on children's lexical retrieval ability

Two alternative accounts have been proposed to explain the role of gestures in thinking and speaking. The Information Packaging Hypothesis (Kita, 2000) claims that gestures are important for the conceptual packaging of information before it is coded into a linguistic form for speech. The Lexical Retrieval Hypothesis (Rauscher, Krauss & Chen, 1996) sees gestures as functioning more at the level of speech production in helping the speaker to find the right words. The latter hypothesis has not been fully explored with children. In this study children were given a naming task under conditions that allowed and restricted gestures. Children named more words correctly and resolved more 'tip-of-the-tongue' states when allowed to gesture than when not, suggesting that gestures facilitate access to the lexicon in children and are important for speech production as well as conceptualization.

The weaker language in early child bilingualism: Acquiring a first language as a second language?

Past research demonstrates that first language (L1)-like competence in each language can be attained in simultaneous acquisition of bilingualism by mere exposure to the target languages. The question is whether this is also true for the “weaker” language (WL). The WL hypothesis claims that the WL differs fundamentally from monolingual L1 and balanced bilingual L1 and resembles second language (L2) acquisition. In this article, these claims are put to a test by analyzing “unusual” constructions in WLs, possibly indicating acquisition failure, and by reporting on analyses of the use of French by bilinguals whose dominant language is German. The available evidence does not justify the claim that WLs resemble L2. Instead, it shows that WL development can be delayed, but does not suggest acquisition failure. Finally, reduced input is unlikely to cause acquisition failure. The fundamental issue at stake is to explore the limits of the human language making capacity.

Testing theories of vowel inherent spectral change

Three competing accounts of vowel inherent spectral change in English all agree on the importance of initial formant frequencies; however, they disagree about the nature of the perceptually relevant aspects of formant change. The onset+offset hypothesis claims that the final formant values themselves matter. The onset+slope hypothesis claims that only the rate of change counts. The onset+direction hypothesis claims that only the general direction of change in formant frequencies is important. A synthetic-vowel perception experiment was designed to differentiate among the three. Results provide support for the superiority of the onset+offset hypothesis.

Analysis of Rotation Curves in the Framework of the Gravitational Suppression Model

We present an analysis of suitable rotation curves (RCs) of eight galaxies, aimed at checking the consistency and universality of the gravitational suppression (GraS) hypothesis, a phenomenological model for a new interaction between dark matter and baryons. Motivated by the puzzle of the core versus cusp distribution of dark matter in the center of halos, this hypothesis claims to reconcile the predictions from N-body Lambda cold dark matter simulations with kinematic observations. The GraS model improves the kinematic fitting residuals, but the mass parameters are unphysical and put the theory in difficulty.

Allopatric Divergence, Secondary Contact, and Genetic Isolation in Wild Yeast Populations

In plants and animals, new biological species clearly have arisen as a byproduct of genetic divergence in allopatry. However, our understanding of the processes that generate new microbial species remains limited [1] despite the large contribution of microbes to the world's biodiversity. A recent hypothesis claims that microbes lack biogeographical divergence because their population sizes are large and their migration rates are presumably high [2, 3]. In recapitulating the classic microbial-ecology dictum that "everything is everywhere, and the environment selects"[4, 5], this hypothesis casts doubt on whether geographic divergence promotes speciation in microbes. To date, its predictions have been tested primarily with data from eubacteria and archaebacteria [6-8]. However, this hypothesis's most important implication is in sexual eukaryotic microbes, where migration and genetic admixture are specifically predicted to inhibit allopatric divergence and speciation [9]. Here, we use nuclear-sequence data from globally distributed natural populations of the yeast Saccharomyces paradoxus to investigate the role of geography in generating diversity in sexual eukaryotic microbes. We show that these populations have undergone allopatric divergence and then secondary contact without genetic admixture. Our data thus support the occurrence of evolutionary processes necessary for allopatric speciation in sexual microbes.

The “Low Dose” Hypothesis: Validity and Implications for Human Risk

In the late 1990s, a "low dose" hypothesis was proposed based on studies that purported to show that hormonally active environmental agents were causing a variety of effects, mainly reproductive and developmental, at "low doses." The supporters of this hypothesis claim that traditional "high-dose" toxicity studies are not adequate to assess adverse effects from these hormonally active agents in that they do not detect effects that are occurring at "low doses." In addition, it is claimed that these "low dose" effects are occurring at levels comparable to those to which humans are being exposed. These claims have been controversial and expert panels evaluated the evidence behind them in the early 2000s. Although these panels generally concluded that such "low dose" effects were not conclusively established, proponents of the "low dose" hypothesis assert that a large number of more recent studies now provide clear support for their hypothesis. This review carefully examines both recent and older studies that have been cited to support the "low dose" hypothesis, including their relevance for the human population. These include in vivo and in vitro laboratory studies as well as a very limited number of epidemiological investigations. Based on the evidence, it is concluded that these "low dose" effects have yet to be established, that the studies purported to support these cannot be validly extrapolated to humans, and the doses at which the studies have been performed are significantly higher than the levels to which humans are exposed.

An inverse relationship between decoration and food colour preferences in satin bowerbirds does not support the sensory drive hypothesis

Male bowerbirds collect and decorate their bowers with coloured objects that influence female choice. A recent version of the sensory drive hypothesis claims that female food colour preferences have driven the evolution of female preferences for the colour of male display traits. This hypothesis predicts a positive correlation between male display and food colour preferences. A positive correlation between food and decoration preferences could also arise because of sensory biases built into bowerbirds or the environment. Here we test hypotheses that (1) male and female satin bowerbirds show well-defined food colour preferences, (2) these preferences correlate with independently assessed preferences for bower decorations, and, in a cross-species comparison, (3) food items were used as the first bower decorations. We found that male and female satin bowerbirds, Ptilonorhynchus violaceus, preferentially use long wavelength and were colours as food items. Male decoration preferences were biased towards colours of short wavelength and were negatively correlated with food colour preferences. Our reconstruction of ancestral character states is most consistent with the hypothesis that the original bower decorations were inedible objects and were thus unlikely to have been dual-use traits that also functioned as food items. Our results do not support the hypothesis that food colour preferences have driven the evolution of bower decoration colour preferences nor that sensory drive has caused similar food and decoration preferences, but instead suggest that different factors have shaped female preferences for male display and food colour preferences in bowerbirds.

Does the error negativity reflect the degree of response conflict?

The recruitment of performance control was recently explained in terms of the detection of response conflict. One recent hypothesis claims that the degree of response conflict is reflected in an electroencephalographical component, the Error Negativity (Ne). Indeed, in the framework of simulations, variations of the Ne fitted well with variations of response conflict. The objective of the present study was to test the conflict hypothesis of the Ne in a real experimental situation. The subjects performed an arrowhead flanker task with two alternative responses. The degree of conflict was measured by the degree of the co-activation of the forces exerted by the two alternative effectors. Trials with co-activations (i.e., an incorrect response activation followed by a correct one) were selected. These trials were divided into two categories, namely trials with suprathreshold error force (full errors) and subthreshold error force (partial errors). The results showed that although the degree of conflict was larger for full than for partial errors, the Ne was not different for the two categories. Our study does not support the hypothesis that the Ne amplitude reflects the degree of conflict.

Inverse association between periodontitis and respiratory allergies

Periodontitis is an infection with systemic effects and a high prevalence among adults. In the aetiology of allergic diseases the hygiene hypothesis claims that infections in early infancy may protect against allergic diseases. The aim of the present analyses was to investigate the independent relation between periodontitis and respiratory allergies such as hayfever, house dust mite (HDM) allergy and asthma. From the Study of Health in Pomerania (SHIP) a total number of 2837 subjects aged 20 to 59 years were included in the analysis. In our study population 326, 111 and 114 subjects were classified as suffering from hayfever, HDM allergy or asthma, respectively. The attachment loss (AL) were measured. Periodontitis was defined according to the percentage of surfaces which exceeded 3 mm AL [healthy: 0-7.7%, mild: 7.8-28.6%, moderate: 28.7-63.9%, severe: >63.9%]. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using logistic regression. After adjustment for confounding factors these analyses revealed inverse associations between periodontitis and hayfever as well as periodontitis and HDM allergy. For increasing AL, a trend of decreasing risk could be observed for hayfever (healthy: reference; mild AL: OR 0.87 [95%-CI 0.6-1.2]; moderate AL: OR 0.80 [95% CI 0.6-1.2]; server AL: OR 0.53 [95% CI 0.3-0.9]; P(trend)=0.01) and for HDM allergy (healthy: reference; mild AL: OR 0.80 [95% CI 0.5-1.3]; moderate AL: OR 0.64 [95% CI 0.3-1.2]; server AL: OR 0.39 [95% CI 0.2-0.9]; P(trend)=0.02). Furthermore, for asthma were observed a slightly inverse association in the full-adjusted model (healthy: reference; mild AL: OR 1.10 [95% CI 0.6-2.0]; moderate AL: OR 0.96 [95% CI 0.5-1.8]; server AL: OR 0.48 [95% CI 0.2-1.0]; P(trend)=0.11). There is an inverse association between periodontitis and respiratory allergies. Our results might support the hygiene hypothesis.

Are mild head injuries as mild as we think? Neurobehavioral concomitants of chronic post-concussion syndrome

BackgroundMild traumatic brain injury (MTBI) can sometimes lead to persistent postconcussion symptoms. One well accepted hypothesis claims that chronic PCS has a neural origin, and is related to neurobehavioral deficits. But the evidence is not conclusive. In the attempt to characterise chronic MTBI consequences, the present experiment used a group comparison design, which contrasted persons (a) with MTBI and PCS, (b) MTBI without PCS, and (c) matched controls. We predicted that participants who have experienced MTBI but show no signs of PCS would perform similar to controls. At the same time, a subgroup of MTBI participants would show PCS symptoms and only these volunteers would have poorer cognitive performance. Thereby, the performance deficits should be most noticeable in participants with highest PCS severity.Method38 patients with a single MTBI that had occurred at least 12 month prior to testing, and 38 matched controls, participated in the experiment. A combination of questionnaires and neuropsychological test batteries were used to assess the extent of PCS and related deficits in neurobehavioral performance.Results11 out of 38 MTBI participants (29%) were found to suffer from PCS. This subgroup of MTBI patients performed poorly on neuropsychological test batteries. Thereby, a correlation was found between PCS symptom severity and test performance suggesting that participants with more pronounced PCS symptoms performed worse in cognitive tasks. In contrast, MTBI patients with no PCS showed performed similar to matched control. We further found that loss of consciousness, a key criterion for PCS diagnosis, was not predictive of sustained PCS.ConclusionThe results support the idea that MTBI can have sustained consequences, and that the subjectively experienced symptoms and difficulties in everyday situations are related to objectively measurable parameters in neurocognitive function.

Development of visual motion perception in children of patients with schizophrenia and bipolar disorder: A follow-up study

The “dorsal-stream vulnerability” hypothesis claims that motion-sensitive areas in the dorsal occipito-parietal visual system are vulnerable to genetic and environmental factors which affect brain maturation and development. The aim of this study was to investigate the possibility that developmental anomalies of directional motion perception can be detected in children of mothers with schizophrenia and bipolar disorder. Motion and form coherence thresholds were measured in 36 children of mothers with schizophrenia, 28 children of mothers with bipolar disorder, and 30 children with negative family history at 7, 8–9, and 10–11 years of age. These tasks require the detection of direction of coherently moving dots embedded among randomly oscillating dots (motion task) and the detection of tangentially oriented line-segments embedded among randomly oriented segments (form task). Results revealed that the rate of development in the motion task was less pronounced in children of mothers with schizophrenia than that in children of mothers with bipolar disorder and in age-matched controls. The development of form perception was spared. Children of mothers with bipolar disorder showed an intact development in both motion and form perception tasks. These results suggest that the progressive developmental abnormality of motion-sensitive visual areas may be a characteristic feature of schizophrenia-vulnerability.

Tracking the what and why of speakers’ choices: Prosodic boundaries and the length of constituents

The rational speaker hypothesis (Clifton, Carlson, & Frazier, 2002) claims that speakers are self-consistent, employing intonation in a manner consistent with their intended message. Preceding a constituent by a prosodic boundary that is not required by the grammar often signals that this constituent is not part of the immediately preceding phrase. However, speakers tend to place prosodic boundaries before and after long constituents. The question is whether prosodic boundaries will have a larger influence on listeners' choice of an analysis when they flank short constituents than when they flank long ones. The results of two listening experiments indicate that they do, suggesting that listeners attend not just to properties of the input signal, but also to the reasons why speakers produce those properties.

Precautionary Regulation in Europe and the United States: A Quantitative Comparison

Much attention has been addressed to the question of whether Europe or the United States adopts a more precautionary stance to the regulation of potential environmental, health, and safety risks. Some commentators suggest that Europe is more risk-averse and precautionary, whereas the United States is seen as more risk-taking and optimistic about the prospects for new technology. Others suggest that the United States is more precautionary because its regulatory process is more legalistic and adversarial, while Europe is more lax and corporatist in its regulations. The flip-flop hypothesis claims that the United States was more precautionary than Europe in the 1970s and early 1980s, and that Europe has become more precautionary since then. We examine the levels and trends in regulation of environmental, health, and safety risks since 1970. Unlike previous research, which has studied only a small set of prominent cases selected nonrandomly, we develop a comprehensive list of almost 3,000 risks and code the relative stringency of regulation in Europe and the United States for each of 100 risks randomly selected from that list for each year from 1970 through 2004. Our results suggest that: (a) averaging over risks, there is no significant difference in relative precaution over the period, (b) weakly consistent with the flip-flop hypothesis, there is some evidence of a modest shift toward greater relative precaution of European regulation since about 1990, although (c) there is a diversity of trends across risks, of which the most common is no change in relative precaution (including cases where Europe and the United States are equally precautionary and where Europe or the United States has been consistently more precautionary). The overall finding is of a mixed and diverse pattern of relative transatlantic precaution over the period.

Perhaps correlational but not causal: No effect of dyslexic readers’ magnocellular system on their eye movements during reading

During reading, dyslexic readers exhibit more and longer fixations and a higher percentage of regressions than normal readers. It is still a matter of debate, whether these divergent eye movement patterns of dyslexic readers reflect an underlying problem in word processing or whether they are – as the proponents of the magnocellular deficit hypothesis claim – associated with deficient visual perception that is causal for dyslexia. To overcome problems in the empirical linkage of the magnocellular theory with reading, a string processing task is presented that poses similar demands on visual perception (in terms of letter identification) and oculomotor control as reading does. Two experiments revealed no differences in the eye movement patterns of dyslexic and control readers performing this task. Furthermore, no relationship between the functionality of the participants’ magnocellular system assessed by the coherent motion task and string processing were found. The perceptual and oculomotor demands required during string processing were functionally equivalent to those during reading and the presented consonant strings had similar visual characteristics as reading material. Thus, a strong inference can be drawn: Dyslexic readers do not seem to have difficulties with the accurate perception of letters and the control of their eye movements during reading – their reading difficulties therefore cannot be explained in terms of oculomotor and visuo-perceptual problems.

OPTIMAL COGNITIVE DISTANCE AND ABSORPTIVE CAPACITY.

Our study tests hypotheses concerning the relation between innovative performance and cognitive distance in inter-firm alliances. The central hypothesis is that performance is an inverted-U shaped function of cognitive distance, which implies a certain optimal cognitive distance. A second hypothesis claims that optimal cognitive distance is higher for exploratory than for exploitative learning. A third hypothesis claims that optimal cognitive distance is a function of absorptive capacity, which depends on cumulative past R&D. Most hypotheses are confirmed on the basis of data from 994 alliances in a variety of industries, in the ten-year period 1986-1996. The results indicate a new hypothesis that with a large stock of knowledge one needs greater cognitive distance for further novelty.