Access Hypothesis Research Articles

Impact of accessibility and chemical composition on cell wall polysaccharide degradability of maize and lucerne stems

Although lignification of forages is generally accepted as limiting cell wall degradability, prediction of degradation from cell wall composition is often difficult when forages are of similar maturity. It has been proposed that rumen microbe accessibility to potentially degradable cell walls is limited by the presence of non-disrupted cells in forage particles with lignified middle lamella/primary walls acting as barriers to microbial access. We tested this accessibility hypothesis by evaluating the impact of reducing particle size of maize and lucerne stems to the level of individual cells by ball-milling, in order to eliminate accessibility as a limiting factor. While cell wall concentration and composition were not influenced by ball-milling compared with grinding to pass a 1 mm screen in a cyclone-type mill, degradability of total cell wall polysaccharides was dramatically increased. However, only those polysaccharides (cellulose and xylan) which are most abundant in cell types with lignified middle lamella/primary and secondary walls increased in degradability owing to particle size reduction. Degradability of pectins, which are abundant in non-lignified tissues in lucerne, did not respond to ball-milling. Contrary to our expectations, ball-milled forages showed fewer correlations for cell wall composition with degradability than observed for the larger-particle-size grinding treatment. Many components of the cell wall were correlated with polysaccharide degradation for the cyclone-ground samples; however, the results were inconsistent as to which cell wall components were correlated with degradation among and within forages. This observation does not clarify the role of cell wall chemical structure as a limiting agent to wall degradation in the absence of accessibility barriers, but this study does provide support for the hypothesis that lignified middle lamella/primary walls act as barriers to microbial access for degradation.

Sex ratios and sexual selection in socially monogamous zebra finches

An experiment was performed in which adult sex ratios of zebra finches, Taeniopygyia guttata castanotis, were varied to test possible effects of adult population sex ratios on sexual selection intensity and mating system dynamics in species with biparental care. The possibility that sex ratio influences the success of social mating patterns (leading to polygyny when males are rare and polyandry when females are rare) was not supported. Results did support the prediction of the differential allocation hypothesis that individuals of the abundant sex would increase their relative parental expenditure (PE). Although total (male + female) PE did not vary between treatments, relative male PE was significantly higher in the male-biased treatment (MBT; sex ratio 64% male) than in the female-biased treatment (FBT; sex ratio 36% male). In both treatments, male PE contributions contributed to female reproductive rate. Results also supported the prediction of the differential access hypothesis that individuals of the abundant sex would experience greater intensity of selection on sexually selected attributes. Male beak color, a sexually selected trait, influenced male social parentage in the MBT but not in the FBT. Finally, broods in the FBT displayed higher hatching asynchrony and lower hatching success; we believe this was caused by early onset of incubation, a tactic used as a defense against intraspecific brood parasitism, which was much higher in the FBT. Population sex ratios may be an important factor affecting female ability to influence male parental investment patterns.

Mechanisms of insulin-like growth factor regulation of programmed cell death of developing avian motoneurons

During development of the avian neuromuscular system, lumbar spinal motoneurons (MNs) innervate their muscle targets in the hindlimb coincident with the onset and progression of MN programmed cell death (PCD). Paralysis (activity blockade) of embryos during this period rescues large numbers of MNs from PCD. Because activity blockade also results in enhanced axonal branching and increased numbers of neuromuscular synapses, it has been postulated that following activity blockade, increased numbers of MNs can gain access to muscle-derived trophic agents that prevent PCD. An assumption of the access hypothesis of MN PCD is the presence of an activity-dependent, muscle-derived sprouting or branching agent. Several previous studies of sprouting in the rodent neuromuscular system indicate that insulin-like growth factors (IGFs) are candidates for such a sprouting factor. Accordingly, in the present study we have begun to test whether the IGFs may play a similar role in the developing avian neuromuscular system. Evidence in support of this idea includes the following: (a) IGFs promote MN survival in vivo but not in vitro; (b) neutralizing antibodies against IGFs reduce MN survival in vivo; (c) both in vitro and in vivo, IGFs increase neurite growth, branching, and synapse formation; (d) activity blockade increases the expression of IGF-1 and IGF-2 mRNA in skeletal muscles in vivo; (e) in vivo treatment of paralyzed embryos with IGF binding proteins (IGF-BPs) that interfere with the actions of endogenous IGFs reduce MN survival, axon branching, and synapse formation; (f) treatment of control embryos in vivo with IGF-BPs also reduces synapse formation; and (g) treatment with IGF-1 prior to the major period of cell death (i.e., on embryonic day 6) increases subsequent synapse formation and MN survival and potentiates the survival-promoting actions of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) administered during the subsequent 4- to 5-day period of PCD. Collectively, these data provide new evidence consistent with the role of the IGFs as activity-dependent, muscle-derived agents that play a role in regulating MN survival in the avian embryo.

The emergence of tense and agreement in child L2 French

The present study examined the acquisition of tense and agreement by L2 learners of French. We looked at whether the features and and the categories AGRP and TP emerged simultaneously or in sequence in the learners' grammars.We conducted interviews with English-speaking children acquiring French as a second language and with grade-matched native-speaker controls once a year for three years. The data were analysed for the productive use of morphosyntax encoding tense and agreement. Results revealed that items encoding agreement emerged before items encoding tense, suggesting that the abstract grammatical structures associated with these morphosyntax items emerge in sequence. The findings are interpreted with respect to three prevailing views on the acquisition of functional phrase structure in L2 acquisition: the Lexical Transfer/Minimal Trees hypothesis (Vainikka and Young-Scholten, 1994; 1996a; 1996b), the Weak Transfer/Valueless Features hypothesis (Eubank, 1993/94; 1994; 1996) and the Full Transfer/Full Access hypothesis (Schwartz and Sprouse, 1994;1996). Possible reasons for the existence of this acquisition sequence in French are also discussed.

De Wet Van Behoud Van Structuur

his paper deals with the L2 conservation hypothesis. It is argued that, in its initial stages, adult L2 acquisition is primarily determined by the LI grammatical system. The acquisition model presented here is in line with the Full Transfer/Full Access hypothesis of Schwartz and Sprouse but is more specific as for the terms transfer (= conservation) and access, and as for the development of morphology. The learner is using his LI system with a target language vocabulary, which has the paradoxical consequence that the LI impact seems to grow the more L2 the learner acquires. This pattern is illustrated by the acquisition of possessive structures by Turkish and Moroccan adults learning Dutch outside the classroom. They appear to act as linguistically conservative individuals who, initially, generate L2 possessive structures by combining their LI grammatical with their limited L2 vocabulary. Consequently, the Turkish and Moroccan learners have different paths of acquisition. They are similar, however, on a more abstract level. Both groups are able to learn specific new parametric values quite early in the acquisition process, and they both have extreme difficulties in learning L2 morphology.

Caricature Recognition in a Neural Network

In a caricature drawing, the artist graphically exaggerates those features of an individual in proportion to their deviations from the normative or average face. The paradox of caricature recognition is that subjects recognize these distorted drawings of faces better than or equally as well as veridical drawings. The present research explores the caricature paradox by modelling caricature recognition in a neural network. Simulations were used to investigate the perceptual versus memorial bases of caricature recognition (Simulation 1) and examine the effects that familiarity (Simulation 2) and typicality (Simulation 3) have on caricature recognition. Simulation results are interpreted as support for a distinctive access hypothesis of the caricature recognition paradox that emphasizes the interaction between the stimulus properties of the caricature drawing and the underlying veridical face representation.

Full access to the evidence for falsification

AbstractThe Epstein, Flynn, and Martohardjorno full access hypothesis could be enhanced by inclusion of criteria for falsification.

The Production of Specific and Generic Associates of Living and Nonliving, High- and Low-Familiarity Stimuli in Alzheimer's Disease

The goal of this paper was to address three issues relevant to the semantic–lexical deficit of Alzheimer's disease (AD) patients: (1) the nature of the deficit (contrasting the loss of information with the difficulty of intentional access hypothesis), (2) stimulus familiarity effects, (3) semantic category effects (contrasting living with nonliving categories). Sixteen patients affected by AD and 11 matched control subjects were given a naming task, a word–picture matching task and a generative associative naming task, constructed by using as stimuli the same 40 items. Stimuli were either living or nonliving items of high, medium, and low familiarity. Responses given on the generative associative naming task were classified as generic (poorly informative) or specific (more informative). As expected, AD patients were poorer than controls both in naming and in word-to-picture matching tasks. In the generative associative naming task, AD patients tended to produce fewer specific than generic associations with respect to controls. Category effects had a significant influence on performance only on the naming task, but not on the word-to-picture matching or on the generative associative naming task. Stimulus familiarity, on the other hand, strongly influenced performance both in AD patients and in controls: naming and comprehension were better for high familiarity items with respect to low familiarity items. For generative associative naming, the tendency of AD patients to produce fewer specific than generic associations was mainly significant for low familiarity items.

Negation in early German-English Interlanguage: more Valueless Features in the L2 initial state

In Eubank (1993/94), I argued that the apparent syntactic optionality one observes in, for example, the placement of medial adverbs vis-à-vis thematic verbs in French-English Interlanguage can be explained if one assumes that the relevant parametric values of French do not transfer into the English L2 initial state. What one finds instead is a nonvalue of sorts, which I dubbed <inert>. In this article, I extend this view of 'Valueless Features' by examining data from Wode (1981) on the L2 acquisition of English by speakers of German. In fact, what I show here is that, in spite of important differences between the French-English and the German-English data, Valueless Features extends in a fairly natural way. In addition, however, I also examine two views that differ from Valueless Features, namely, the Full Transfer/Full Access Hypothesis of Schwartz and Sprouse (e.g., 1994) and the Minimal Trees of Vainikka and Young-Scholten (1994). Here, a careful review of the acquisitional data - either the French-English data or the German-English data - suggests that these views may not be as straightforward as they may otherwise appear.

Weak Mate Guarding in Tree Swallows: Ecological Constraint or Female Control?

AbstractWe re‐examined tree swallows (Tachycineta bicolor) for the presence of the paternity protection tactic of mate guarding using less conservative criteria for its detection than did an earlier study. Our results are consistent with weak mate guarding, but may also be explained by the copulatory access hypothesis. The latter hypothesis suggests that the spatio‐temporal demands of pair copulation can result in a similar pattern of behaviour to mate guarding. We address two hypotheses advanced previously for the lack of intense mate guarding in this species as compared with other species. These are that female fidelity obviates the need for males to mate guard, and that the risk of nest site usurpation prevents males from guarding. Since tree swallows have one of the highest known rates of extra‐pair paternity, the first hypothesis is discounted. We find the second hypothesis unlikely after an examination of the species' ecology, and suggest an alternative hypothesis to account for the lack of intense guarding. In short, we propose that in species such as tree swallows, in which females appear to have a significant degree of interest in, and control over, extra‐pair fertilizations, frequent copulation may be a more cost‐efficient means of ensuring paternity than is mate guarding.

Processing Ambiguous Words in Context

Tabossi (1988) described data suggesting that both dominance and context may have an effect on access to lexical ambiguity. Experiments 1 and 2 here extend those results, showing that the selective findings observed in that study are not due to an exhaustive access followed by a fast selection, but reflect genuine context effects. In the light of these findings, a time-course hypothesis of lexical access is introduced, and its explanatory capacity relative to current theories is discussed.

Expectancy Accessibility and the Influence of Outcome Expectancies on Adolescent Smokeless Tobacco Use

This study investigated the moderating influence of expectancy accessibility on the relation between outcome expectancies and drug use intentions. Specifically, it was hypothesized that expectancies made temporarily more accessible would predict smokeless tobacco intentions to a greater degree than would less accessible expectancies. In addition, it was anticipated that expectancies regarding positive outcomes of smokeless tobacco use would be better predictors of intention than would expectancies about negative outcomes. Results partially supported the accessibility hypothesis, but this effect occurred for positive outcome expectancies only. In addition, the anticipated prepotency of positive over negative expectancies in predicting drug use intentions was strongly supported. These findings are consistent with theories of problem behavior which differentiate between positive and negative outcome expectancies and which postulate that accessibility of expectancies plays an important role in expectancy‐behavior relations.

Attitude Importance and Attitude Accessibility

Across a range of settings, attitudes that people consider personally important have been shown to be more powerful determinants of perceptions of others' attitudes, of liking of others, and of social behavior than unimportant attitudes are. This article reports two studies that evaluate one possible explanation for this difference: the hypothesis that important attitudes may be more accessible in memory and may therefore come to mind more frequently in the course of social perception. In both studies, subjects reported the importance they attached to a series of political attitudes and reported those attitudes on a computer that measured response latencies. Important attitudes were reported more quickly than unimportant ones, even when subjects were instructed to report the first attitudinal cue that came to mind. This finding supports the accessibility hypothesis.

Processing of lexical ambiguities: A comment on Milberg, Blumstein, and Dworetzky (1987)

In a study by Milberg, Blumstein, and Dworetzky (1987), normal control subjects and Wernicke's and Broca's aphasics performed a lexical decision task on the third element of auditorily presented triplets of words with either a word or a nonword as target. In three of the four types of word triplets, the first and the third words were related to one or both meanings of the second word, which was semantically ambiguous. The fourth type of word triplet consisted of three unrelated, unambiguous words, functioning as baseline. Milberg et al. (1987) claim that the results for their control subjects are similar to those reported by Schvaneveldt, Meyer, and Becker's original study (1976) with the same prime types, and so interpret these as evidence for a selective lexical access of the different meanings of ambiguous words. It is argued here that Milberg et al. only partially replicate the Schvaneveldt et al. results. Moreover, the results of Milberg et al. are not fully in line with the selective access hypothesis adopted. Replication of the Milberg et al. (1987) study with Dutch materials, using both a design without and a design with repetition of the same target words for the same subjects led to the original pattern as reported by Schvaneveldt et al. (1976). In the design with four separate presentations of the same target word, a strong repetition effect was found. It is therefore argued that the discrepancy between the Milberg et al. results on the one hand, and the Schvaneveldt et al. results on the other, might be due to the absence of a control for repetition effects in the within-subject design used by Milberg et al. It is concluded that this makes the results for both normal and aphasic subjects in the latter study difficult to interpret in terms of a selective access model for normal processing.

Word recognition in early reading: A review of the direct and indirect access hypotheses

Research on the development of word recognition, like that on fluent word recognition, has been strongly influenced by the dual-route model. One route is non-lexical and indirect because access to lexical meaning is mediated by pre-lexical phonological representations assembled through the application of grapheme-to-phoneme correspondence (GPC) rules. The other route, which is independent of the first, is regarded as lexical and direct because orthographic representations of whole words are used to retrieve lexical meanings or post-lexical phonological representations. Evidence is reviewed for two opposing developmental hypotheses based on the dual-route model: fluent readers use both direct and indirect access to lexical meaning, while beginning readers use (1) only indirect access or (2) only direct access. It was concluded that neither mode of access predominates in early reading. A review of other evidence suggests two reasons why the dual-route model fails to provide a satisfactory account of the development of early word recognition. First, it does not offer an adequate characterization of the orthographic units represented in early lexicons. Second, the independence of the two routes prevents lexical information from being acquired through the application of GPC rules. Finally, alternatives to the dual-route model are discussed. One of the most promising is a single process lexical model in which it is proposed that acquisition and performance in word recognition can be accounted for by interactions among orthographic and phonological units of various sizes in the lexicon.

Time-average optimal constrained semi-Markov decision processes

Optimal causal policies maximizing the time-average reward over a semi-Markov decision process (SMDP), subject to a hard constraint on a time-average cost, are considered. Rewards and costs depend on the state and action, and contain running as well as switching components. It is supposed that the state space of the SMDP is finite, and the action space compact metric. The policy determines an action at each transition point of the SMDP.Under an accessibility hypothesis, several notions of time average are equivalent. A Lagrange multiplier formulation involving a dynamic programming equation is utilized to relate the constrained optimization to an unconstrained optimization parametrized by the multiplier. This approach leads to a proof for the existence of a semi-simple optimal constrained policy. That is, there is at most one state for which the action is randomized between two possibilities; at all other states, an action is uniquely chosen for each state. Affine forms for the rewards, costs and transition probabilities further reduce the optimal constrained policy to ‘almost bang-bang’ form, in which the optimal policy is not randomized, and is bang-bang except perhaps at one state. Under the same assumptions, one can alternatively find an optimal constrained policy that is strictly bang-bang, but may be randomized at one state. Application is made to flow control of a birth-and-death process (e.g., an M/M/s queue); under certain monotonicity restrictions on the reward and cost structure the preceding results apply, and in addition there is a simple acceptance region.

Time-average optimal constrained semi-Markov decision processes

Optimal causal policies maximizing the time-average reward over a semi-Markov decision process (SMDP), subject to a hard constraint on a time-average cost, are considered. Rewards and costs depend on the state and action, and contain running as well as switching components. It is supposed that the state space of the SMDP is finite, and the action space compact metric. The policy determines an action at each transition point of the SMDP. Under an accessibility hypothesis, several notions of time average are equivalent. A Lagrange multiplier formulation involving a dynamic programming equation is utilized to relate the constrained optimization to an unconstrained optimization parametrized by the multiplier. This approach leads to a proof for the existence of a semi-simple optimal constrained policy. That is, there is at most one state for which the action is randomized between two possibilities; at all other states, an action is uniquely chosen for each state. Affine forms for the rewards, costs and transition probabilities further reduce the optimal constrained policy to ‘almost bang-bang’ form, in which the optimal policy is not randomized, and is bang-bang except perhaps at one state. Under the same assumptions, one can alternatively find an optimal constrained policy that is strictly bang-bang, but may be randomized at one state. Application is made to flow control of a birth-and-death process (e.g., an M/M/s queue); under certain monotonicity restrictions on the reward and cost structure the preceding results apply, and in addition there is a simple acceptance region.

Semantic and phonological strategies for anagram construction in dyslexic children.

Children with developmental dyslexia do evince, in reading, a number of different types of behavior: a) they often read words and sentences without understanding them; b) they have particular difficulty in reading words devoid of sense; c) they frequently make up endings for the words they are reading; d) they are unable to pin down the error in a mistaken word. If considered together, all these types of behavior correspond to two fundamental strategies: 1) at times the dyslexic child ascribes meanings to words or segments of words that have meaning; 2) at times the dyslexic child is unable to ascribe a meaning, or the correct meaning, to words or segments of words, that have meaning. These two strategies may be considered as two antithetical answers to the same problem: a) how to connect written words to their meanings, departing from their auditory representation (phonological access) and/or their visual representation (visual access); b) how to coordinate processes of conversion from graphemes to phonemes (in either case without semantic meaning) with the aim of reading, giving a semantic meaning to what is read. Over the last ten years, the question of the relationships between written language and oral language has been considered from a number of very different standpoints, and theories on the pathogenesis of developmental dyslexia have been greatly influenced by the way this problem has been formulated (Benton, 1975; Rutter and Yule, 1975; Rourke, 1976; Mattis, 1978; Vellutino, 1979a; Jorm, 1979a; Shallice and Warrington, 1980). A) There was some question as to whether or not dyslexic children encounter a specific difficulty in the conversion from phonemes to graphemes. Departing from this formulation it was thought: either that the dyslexic child has prejudicial difficulties in recognizing, categorizing, and combining the graphemes in sequences (visuo-perceptual hypothesis) (Kerschner, 1975; Clifton-Everest, 1976; Fletcher and Satz, 1979; Lovegrove et al., 1980), or that the dyslexic child will encounter prejudicial difficulties in composing or breaking up words into phonemes (linguistic hypothesis) (Liberman et al., 1977; Fischer et al., 1978; Levi and Musatti, 1978; Vellutino, 1979). B) There was some question as to whether dyslexic children find it difficult to globalize written words and work them into a structure of meanings (Denkla and Rudel, 1976 a-b; Coltheart, 1978; Saffran, 1980). Departing from this formulation, it was thought: either that the dyslexic child doesn't know how to connect the written word to its auditory representation (hypothesis of phonological access) (Patterson, 1978; Jorm, 1979b), or that the dyslexic child doesn't know how to connect the written word directly to the corresponding concept (hypothesis of direct visual access) (Ellis, 1979; Holmes, 1978). As we have already indicated, in order to read it is necessary to find one sole answer to two types of problems: a) to tie the written word to a linguistic meaning; b) to coordinate processes of conversion from graphemes to phonemes, with the aim of reading with meaning. Theories on the pathogenesis of developmental dyslexia are distinguished in accordance with how these two individual questions are considered, and how the relationships between the two types of problems is explained. 1) For some authors reading is first and foremost a process of visual transcription of oral language (Bouma and Legein, 1980; Carr Payne et al., 1980); once a biunivocal correspondence between graphemes and phonemes is established, and that the graphemes can be globalized into words, according to these authors, the problem of ascribing a meaning to the written word is for the most part posed if not solved. 2) For some authors reading is as much a process of cognitive-semantic construction as oral language is (Gibson and Levin, 1975; Ferreiro, 1976; Lentin, 1978). Those who read foresee individual graphemes and syllables on a basis of precise semantic hypotheses; in these authors view, the conversion from graphemes into phonemes is only one particular example of phonological categorizing. The outline we have just examined describes only the broad contours of a complex debate on this topic. What most concerns us is the pinning down of the linguistic-cognitive paradox of reading (Levi et al., 1979; Levi et al., 1981): a) in order to master reading it is necessary to know how to convert graphemes into phonemes (individually and in sequence) even in the absolute sense, that is to say irrespective of the quest for, or the hooking up with a semantic meaning; which explains the complexity that marks the reading of words without meaning, or with a meaning that is unknown; b) in order to master reading it is necessary to advance semantic hypotheses with regard to what is read, and to check the congruence between the assumed word and the real word: which explains the complexity that marks the task of singling out individual errors in wrong words.

Optimal policies for controlled Markov chains with a constraint

The time average reward for a discrete-time controlled Markov process subject to a time-average cost constraint is maximized over the class of al causal policies. Each epoch, a reward depending on the state and action, is earned, and a similarly constituted cost is assessed; the time average of the former is maximized, subject to a hard limit on the time average of the latter. It is assumed that the state space is finite, and the action space compact metric. An accessibility hypothesis makes it possible to utilize a Lagrange multiplier formulation involving the dynamic programming equation, thus reducing the optimization problem to an unconstrained optimization parametrized by the multiplier. The parametrized dynamic programming equation possesses compactness and convergence properties that lead to the following: If the constraint can be satisfied by any causal policy, the supremum over time-average rewards respective to all causal policies is attained by either a simple or a mixed policy; the latter is equivalent to choosing independently at each epoch between two specified simple policies by the throw of a biased coin.

A Shift from Phonological Recoding to Direct Access in Reading as a Result of Previous Exposure

The present study examined the effect of repeated exposures of a visually presented phrase on the mode of lexical access (phonological recoding vs. visual mediation) used. Subjects made meaningfulness decisions about two- and three-word phrases. Following five exposures to each phrase, some of which sounded meaningful but were not (“drops of do”), and others which were neither (“nut and bout”), the significant reaction time advantage on the first exposure for rejecting the latter phrase type was eliminated. Results supported the dual access hypothesis that subjects use phonological recoding upon initial exposure to a phrase, but following repeated exposures are able to use direct visual access. A dual access model compatible with these results is discussed.