Evaluation of management factors affecting the relative success of a Brook Trout eradication program using YY male fish and electrofishing suppression

Removal of non-native fish populations can be crucial to the conservation of native species, but often presents a complex challenge for managers. The goal of Trojan Y chromosome (TYC) programs is to skew the non-native sex ratio until only males remain, leading to eradication. We present results from a simulation model used to explore effects of alternative management approaches on an in-progress mechanical removal and TYC program to eradicate non-native Brook Trout. Simulation results indicated that stocking fingerling YY males (~137 mm) was more effective than stocking catchable-sized YY males (~230 mm), although questions about inter-cohort competition warrant further investigation. Increasing the proportion of mature fingerling YY males reduced treatment time by increasing the number of YY male spawners and increasing density-dependent mortality on young, mature wild Brook Trout. Maximizing the spatial distribution of YY male releases may be crucial to program success but is also dependent upon immediate dispersal movements. Principles derived from our results can be broadly applied to the management of other aquatic invaded systems using TYC programs to eradicate non-native species.

How does(n't) syntactic context guide auditory word recognition?

Better understanding of word recognition requires a detailed account of how top-down and bottom-up information are integrated. In this paper, we use a combination of modeling and experimental work to investigate the mechanism by which expectations from syntactic context influence the processing of perceptual input during word recognition. The distinction between facilitatory and inhibitory mechanisms for the syntactic category constraint is an important aspect of this problem that has previously been underspecified, and syntactic category is a relatively simple test case for the issue of context in other domains. We first report simulations in jTRACE that point to an explanation for conflicts that have occurred between different methods regarding the existence and timing of syntactic constraints on lexical cohort competition. We show that the composition of the set of response candidates allowed by the task is predicted to influence whether and when changes in lexical activation can be observed in dependent measures, which is relevant for the design and interpretation of experiments involving cohort competition more broadly. These insights informed a new design for the visual world paradigm that distinguishes facilitatory and inhibitory mechanisms and ensures that activation of words from the wrong syntactic category should be detectable if it is occurring. We demonstrate how failure to ensure this could have obscured such activation in previous work, leading to the appearance of an inhibitory constraint. We find that wrong-category competition does occur, a result that is incompatible with an inhibitory syntactic category constraint.

Lexical Access Changes Based on Listener Needs: Effects of Sentence Context on Real-Time Word Recognition in Cochlear Implant Users

ObjectivesOne key challenge in word recognition is the temporary ambiguity in the signal created by the fact that speech unfolds over time. Research with normal hearing (NH) listeners reveals that this temporary ambiguity is resolved through incremental processing of the signal and competition among possible lexical candidates. Post-lingually deafened cochlear implant (CI) users show similar incremental processing and competition to NH listeners but with slight delays. However, even brief delays could lead to drastic changes when compounded across multiple words in a sentence. This study asks whether words presented in non-informative sentence contexts are processed differently than words presented in isolation and whether any differences are shared among NH listeners and CI users or if the groups exhibit different patterns.DesignAcross two visual world paradigm experiments, listeners heard words presented either in isolation or in non-informative sentence contexts (“click on the…”). Listeners selected the picture corresponding to the target word from among four items including the target word (e.g., mustard), a cohort competitor (e.g., mustache), a rhyme competitor (e.g., custard), and an unrelated item (e.g., penguin). During this task, eye movements were tracked as an index of the relative lexical activation of each object type during word recognition. Subjects included 65 CI users and 48 NH controls across both experiments. ResultsBoth CI users and the NH controls were largely accurate at recognizing the words both in sentence contexts and in isolation. The time course of lexical activation (indexed by the fixations) differed substantially between groups. CI users were delayed in fixating the target relative to NH controls. Additionally, CI users showed less competition from cohorts (while previous studies have often found increased competition) compared to NH controls. However, CI users took longer to suppress the cohort and suppressed it less fully than the NH controls. For both CI users and NH controls, embedding words in sentences led to more immediacy in lexical access as observed by increases in cohort competition relative to when words were presented in isolation. However, CI users were not differentially affected by the sentencesConclusionsUnlike prior work, in both sentences and in isolated words CI users appeared to exhibit “wait-and-see” strategy, in which lexical access is delayed to minimize early competition. However, they simultaneously sustain competitor activation late in the trial possibly to preserve flexibility. This hybrid profile has not been observed previously. Both CI users and NH controls more heavily weight early information when target words are presented in sentence contexts. However, CI users (but not NH listeners) also commit less fully to the target when words are presented in sentence context potentially keeping options open if they need to recover from a misperception. This mix of patterns reflects a lexical system that is extremely flexible and adapts to fit the needs of a listener.

Decompositional Representation of Morphological Complexity: Multivariate fMRI Evidence from Italian

Derivational morphology is a cross-linguistically dominant mechanism for word formation, combining existing words with derivational affixes to create new word forms. However, the neurocognitive mechanisms underlying the representation and processing of such forms remain unclear. Recent cross-linguistic neuroimaging research suggests that derived words are stored and accessed as whole forms, without engaging the left-hemisphere perisylvian network associated with combinatorial processing of syntactically and inflectionally complex forms. Using fMRI with a “simple listening” no-task procedure, we reexamine these suggestions in the context of the root-based combinatorially rich Italian lexicon to clarify the role of semantic transparency (between the derived form and its stem) and affix productivity in determining whether derived forms are decompositionally represented and which neural systems are involved. Combined univariate and multivariate analyses reveal a key role for semantic transparency, modulated by affix productivity. Opaque forms show strong cohort competition effects, especially for words with nonproductive suffixes (ventura, “destiny”). The bilateral frontotemporal activity associated with these effects indicates that opaque derived words are processed as whole forms in the bihemispheric language system. Semantically transparent words with productive affixes (libreria, “bookshop”) showed no effects of lexical competition, suggesting morphologically structured co-representation of these derived forms and their stems, whereas transparent forms with nonproductive affixes (pineta, pine forest) show intermediate effects. Further multivariate analyses of the transparent derived forms revealed affix productivity effects selectively involving left inferior frontal regions, suggesting that the combinatorial and decompositional processes triggered by such forms can vary significantly across languages.

The Interaction of Lexical Semantics and Cohort Competition in Spoken Word Recognition: An fMRI Study

Spoken word recognition involves the activation of multiple word candidates on the basis of the initial speech input—the “cohort”—and selection among these competitors. Selection may be driven primarily by bottom–up acoustic–phonetic inputs or it may be modulated by other aspects of lexical representation, such as a word's meaning [Marslen-Wilson, W. D. Functional parallelism in spoken word-recognition. Cognition, 25, 71–102, 1987]. We examined these potential interactions in an fMRI study by presenting participants with words and pseudowords for lexical decision. In a factorial design, we manipulated (a) cohort competition (high/low competitive cohorts which vary the number of competing word candidates) and (b) the word's semantic properties (high/low imageability). A previous behavioral study [Tyler, L. K., Voice, J. K., & Moss, H. E. The interaction of meaning and sound in spoken word recognition. Psychonomic Bulletin & Review, 7, 320–326, 2000] showed that imageability facilitated word recognition but only for words in high competition cohorts. Here we found greater activity in the left inferior frontal gyrus (BA 45, 47) and the right inferior frontal gyrus (BA 47) with increased cohort competition, an imageability effect in the left posterior middle temporal gyrus/angular gyrus (BA 39), and a significant interaction between imageability and cohort competition in the left posterior superior temporal gyrus/middle temporal gyrus (BA 21, 22). In words with high competition cohorts, high imageability words generated stronger activity than low imageability words, indicating a facilitatory role of imageability in a highly competitive cohort context. For words in low competition cohorts, there was no effect of imageability. These results support the behavioral data in showing that selection processes do not rely solely on bottom–up acoustic–phonetic cues but rather that the semantic properties of candidate words facilitate discrimination between competitors.