A versatile ultra high vacuum sample stage with six degrees of freedom.

We describe the design and practical realization of a versatile sample stage with six degrees of freedom. The stage was designed for use in a Low Energy Electron Microscope, but its basic design features will be useful for numerous other applications. The degrees of freedom are X, Y, and Z, two tilts, and azimuth. All motions are actuated in an ultrahigh vacuum base pressure environment by piezoelectric transducers with integrated position sensors. The sample can be load-locked. During observation, the sample is held at a potential of -15 kV, at temperatures between room temperature and 1500 °C, and in background gas pressures up to 1 × 10(-4) Torr.

In situ observations of endotaxial growth of CoSi2 nanowires on Si(110) using ultrahigh vacuum transmission electron microscopy.

We report in situ observations of the growth of endotaxial CoSi(2) nanowires on Si(110) using an ultrahigh vacuum transmission electron microscope with a miniature electron-beam deposition system located above the pole-piece of the objective lens. Metal deposition at 750-850 °C results in formation of coherently strained silicide nanowires with a fixed length/width (L/W) aspect ratio that depends strongly on temperature. Both dimensions evolve with time as L, W ∼ t(1/3). To explain this behavior, we propose a fixed-shape growth mode based on thermally activated facet-dependent reactions. A second growth mode is also observed at 850 °C, with dimensions that evolve as L ∼ t and W ∼ constant. This mode is accompanied by formation of an array of dislocations. We expect that other endotaxial nanowire systems will follow coherently strained growth modes with similar geometrical constraints, as well as dislocated growth modes with different growth kinetics.

A new aberration-corrected, energy-filtered LEEM/PEEM instrument. I. Principles and design.

We describe a new design for an aberration-corrected low energy electron microscope (LEEM) and photo electron emission microscope (PEEM), equipped with an in-line electron energy filter. The chromatic and spherical aberrations of the objective lens are corrected with an electrostatic electron mirror that provides independent control over the chromatic and spherical aberration coefficients C(c) and C(3), as well as the mirror focal length, to match and correct the aberrations of the objective lens. For LEEM (PEEM) the theoretical resolution is calculated to be approximately 1.5 nm (approximately 4 nm). Unlike previous designs, this instrument makes use of two magnetic prism arrays to guide the electron beam from the sample to the electron mirror, removing chromatic dispersion in front of the mirror by symmetry. The aberration correction optics was retrofitted to an uncorrected instrument with a base resolution of 4.1 nm in LEEM. Initial results in LEEM show an improvement in resolution to approximately 2 nm.

A simple energy filter for low energy electron microscopy/photoelectron emission microscopy instruments.

Addition of an electron energy filter to low energy electron microscopy (LEEM) and photoelectron emission microscopy (PEEM) instruments greatly improves their analytical capabilities. However, such filters tend to be quite complex, both electron optically and mechanically. Here we describe a simple energy filter for the existing IBM LEEM/PEEM instrument, which is realized by adding a single scanning aperture slit to the objective transfer optics, without any further modifications to the microscope. This energy filter displays a very high energy resolution ΔE/E = 2 × 10(-5), and a non-isochromaticity of ∼0.5 eV/10 µm. The setup is capable of recording selected area electron energy spectra and angular distributions at 0.15 eV energy resolution, as well as energy filtered images with a 1.5 eV energy pass band at an estimated spatial resolution of ∼10 nm. We demonstrate the use of this energy filter in imaging and spectroscopy of surfaces using a laboratory-based He I (21.2 eV) light source, as well as imaging of Ag nanowires on Si(001) using the 4 eV energy loss Ag plasmon.

Traces of vocabulary acquisition in the brain: Evidence from covert object naming.

One of the strongest predictors of the speed with which adults can name a pictured object is the age at which the object and its name are first learned. Age of acquisition also predicts the retention or loss of individual words following brain damage in conditions like aphasia and Alzheimer's disease. Functional Magnetic Resonance Imaging (fMRI) was used to reveal brain areas differentially involved in naming objects with early or late acquired names. A baseline task involved passive viewing of non-objects. The comparison between the silent object naming conditions (early and late) with baseline showed significant activation in frontal, parietal and mediotemporal regions bilaterally and in the lingual and fusiform gyri on the left. Direct comparison of early and late items identified clusters with significantly greater activation for early acquired items at the occipital poles (in the posterior parts of the middle occipital gyri) and at the left temporal pole. In contrast, the left middle occipital and fusiform gyri showed significantly greater activation for late than early acquired items. We propose that greater activation to early than late objects at the occipital poles and at the left temporal pole reflects the more detailed visual and semantic representations of early than late acquired items. We propose that greater activation to late than early objects in the left middle occipital and fusiform gyri occurs because those areas are involved in mapping visual onto semantic representations, which is more difficult, and demands more resource, for late than for early items.

Evaluating a split fovea model of visual word recognition: effects of case alternation in the two visual fields and in the left and right halves of words presented at the fovea.

Two experiments are reported exploring the effect of cAsE aLtErNaTiOn on lexical decisions to words and nonwords presented laterally or centrally. In line with previous research, Experiment 1 found that case alternation slowed lexical decision responses to words more in the right visual field (RVF) than in the left visual field (LVF). In Experiment 2, the words and nonwords were all presented centrally. There were three conditions, a condition in which the word and nonwords were presented in lower case letters, a condition in which the letters to the left of the central fixation were case alternated (e.g., aMbItion, mOdLants) and a condition in which the letters to the right of fixation were case alternated (e.g., collApSe, pireNtOl). Alternating the case of letters to the right of fixation slowed lexical decision responses more than alternating letter case to the left of fixation. The results provide further support for a split fovea account of visual word recognition according to which those letters of a centrally-fixated word that fall to the left of fixation are processed initially by the right cerebral hemisphere while those letters that fall to the right of fixation are processed initially by the left cerebral hemisphere, with the characteristics of the left and right hemispheres being revealed in the processing of initial and final letters in centrally presented words.

Evaluating a split processing model of visual word recognition: effects of word length.

A new theory of visual word recognition is based on the fact that the fovea is split in humans. When a reader fixates the center of a written word, the initial letters of the word that are to the left of fixation are projected first to the right cerebral hemisphere (RH) while the final letters are projected to the left cerebral hemisphere (LH). This paper explores the possibility that this has consequences for the early processing of the beginning and ends of centrally fixated words: specifically that lexical decision RTs are affected by the number of letters to the left of fixation but not by the number of letters to the right of fixation. For centrally presented five- and eight-letter words, we manipulated number of letters presented to the right or to the left of a fixation point (Experiment 1). We found that longer latencies to longer letter strings characterised the processing of the initial letters of words while LH word recognition features characterised the ends of words. Experiment 2 was a lateralized version of Experiment 1, and revealed the well established visual field and word length interaction. The results supported the split fovea theory.

Mixed-case effects in lateralized word recognition.

Effects of case alternation and word length were studied in a lateralized visual lexical decision task. The previously reported visual field and word length interaction was found for upper- and lowercase presentations, but not for MiXeD CaSe, where both fields were affected by word length. We discuss the results in light of two contrasting models of lateralized word recognition.

Age of acquisition effects in adult lexical processing reflect loss of plasticity in maturing systems: insights from connectionist networks.

Early learned words are recognized and produced faster than later learned words. The authors showed that such age of acquisition effects are a natural property of connectionist models trained by back-propagation when patterns are introduced at different points into training and learning of early and late patterns is cumulative and interleaved. Analysis of hidden unit activations indicated that the age of acquisition effect reflects a gradual reduction in network plasticity and a consequent failure to differentiate late items as effectively as early ones. Further simulations examined the effects of vocabulary size, learning rate, sparseness of coding, use of a modified learning algorithm, loss of early items, acquisition of very late items, and lesioning the network. The relationship between age of acquisition and word frequency was explored, including analyses of how the relative influence of these factors is modulated by introducing weight decay.

Perceptual priming is not a necessary consequence of semantic classification of pictures.

Four experiments investigated how repetition priming of object recognition is affected by the task performed in the prime and test phases. In Experiment 1 object recognition was tested using both vocal naming and two different semantic decision tasks (whether or not objects were manufactured, and whether or not they would be found inside the house). Some aspects of the data were inconsistent with contemporary models of object recognition. Specifically, object priming was eliminated with some combinations of prime and test tasks, and there was no evidence of perceptual (as opposed to conceptual or response) priming in either semantic classification task, even though perceptual identification of the objects is required for at least one of these tasks. Experiment 2 showed that even when perceptual demands were increased by brief presentation, the inside task showed no perceptual priming. Experiment 3 showed that the inside task did not appear to be based on conceptual priming either, as it was not primed significantly when the prime decisions were made to object labels. Experiment 4 showed that visual sensitivity could be restored to the inside task following practice on the task, supporting the suggestion that a critical factor is whether the semantic category is preformed or must be computed. The results show that the visual representational processes revealed by object priming depend crucially on the task chosen.

Real age of acquisition effects in word naming and lexical decision.

Age of acquisition (AoA) has been reported to be a predictor of the speed of reading words aloud (word naming) and lexical decision, with early-acquired words being responded to faster than later-acquired words in both tasks. All previous studies of AoA effects have, however, relied upon adult estimates of word learning age the validity of which it is easy to cast doubt upon. Using objective age of acquisition norms derived from children's naming data, this study shows that AoA effects do not depend upon the use of adult ratings. In addition to effects of real AoA, influences of word frequency and orthographic neighbourhood size were obtained in both word naming and lexical decision. Imageability affected lexical decision but not word naming, while the characteristics of the word's initial phoneme affected word naming but not lexical decision.

Pictures of Episcopal hospital, Philadelphia, PA: part I (1851-1926).

The merit of images, often posed, often retouched, as historical documents has been debated by numerous scholars. Nonetheless, portraits, illustrations, and photographs form one of the more delightful avenues for recapturing elements of medical care as it was practiced in the past. Part one of this two-part photo-essay records the first cycles of growth and contraction that characterized the history of one of Philadelphia's foremost medical institutions: The Hospital of the Protestant Episcopal Church of Philadelphia.

Why do some aphasics show an advantage on some tests of nonpropositional (automatic) speech?

Sixteen aphasic patients were given three pairs of tasks that compared the production of the same items in either propositional or nonpropositional contexts. A nonpropositional number production task involved counting from 1 to 10 while the propositional version of that task involved naming the Arabic numbers 1 to 10 in nonconsecutive order. A nonpropositional picture-naming task involved naming pictures with the aid of familiar phrase cues (e.g., Don't beat around the BUSH) while in the propositional version the cues were novel phrases (e.g., Don't dig behind the BUSH). Finally a nonpropositional phrase repetition task involved repeating well-known phrases while the propositional version involved repeating novel phrases. The group as a whole showed strong nonpropositional advantages for number production and picture naming with a somewhat weaker advantage for phrase repetition. Only 5 of the individual patients showed nonpropositional advantages on all three pairs of tasks: the remaining 11 patients showed a significant nonpropositional advantage on one or two of the pairs of tasks, but not on all three. All of the patients showed a nonpropositional advantage on at least one pair of tasks, and there were no examples of better performance on the propositional than on the nonpropositional version of any task. Contrasting patterns of performance seen in different patients was related to their performance on a battery of cognitive and linguistic tasks that was given to each patient.

Visual paralexias in a Spanish-speaking patient with acquired dyslexia: a consequence of visual and semantic impairments?

We report the case of a Spanish patient SC who misread 55 per cent of the single words shown to her. SC's reading accuracy was affected by word imageability and frequency. Nonword reading was very poor. The majority of SC's errors to real-word targets bore a close visual similarity to the items that elicited them, but there was no indication of an effect of serial position on the probability that a letter from a target word would be incorporated into the error made to that word. SC made some visual errors in object naming and also showed evidence of a general semantic impairment. We consider the similarity between SC and patient AB reported by Lambon Ralph and Ellis (1997), and suggest that the very high levels of visual errors shown by these two patients may reflect a combination of visual and semantic impairments.

Naming times for the Snodgrass and Vanderwart pictures in Spanish.

We present new Spanish norms for object familiarity and rated age of acquisition for 140 pictures taken from Snodgrass and Vanderwart (1980), together with data on visual complexity, image agreement, name agreement, word length (in syllables and phonemes), and five measures of word frequency. The pictures were presented to a group of 64 Spanish subjects, and oral naming latencies were recorded. In a multiple regression analysis, age of acquisition, object familiarity, name agreement, word frequency, and word length made significant independent contributions to predicting naming latency.

Contrasting effects of age of acquisition and word frequency on auditory and visual lexical decision.

In four experiments, we examined the effects of frequency and age of acquisition on auditory and visual lexical decision. Word frequency affected visual, but not auditory, lexical decision speed (Experiments 1 and 3). Age of acquisition affected lexical decision speed in both modalities (Experiments 2 and 4). We suggest that previous reports of effects of frequency on auditory lexical decision may be due to a confounding of frequency with age of acquisition, and we discuss the implications of these findings for theories of auditory and visual word recognition.

Naming in semantic dementia--what matters?

One of the major symptoms of semantic dementia (or progressive fluent aphasia) is profound word-finding difficulties. We present here a cross-sectional study of the factors affecting picture naming in semantic dementia based on data obtained from eight patients, together with a longitudinal analysis of naming in another patient. Various properties and attributes of the objects were entered into a series of regression analyses in order to predict which items the patients could or could not name. The analyses showed that object familiarity, word frequency and age-of-acquisition predicted naming success for the group and, in most cases, for each individual patient, irrespective of lesion site or overall naming success. We propose that the pattern of naming in semantic dementia is best described in terms of reduced semantic activation within a cascading/interactive speech production system. We suggest that object familiarity, and possibly word frequency, reflect the inherent robustness of individual semantic representations to the decay process in terms of both quantity and quality of experience. Age-of-acquisition and word frequency (at a phonological-lexical level) predicts naming success, because frequent, early-acquired words are relatively easy to activate even with reduced semantic "input".

Last in, first to go: age of acquisition and naming in the elderly.

Twenty-six elderly subjects (ages 71-86) and 10 young adult subjects (ages 22-33) named 206 black-and-white line drawings of objects. Although the two groups did not differ significantly on VIQ, the elderly group named significantly fewer of the objects than the younger group (who were almost at ceiling). A regression analysis of the data from the elderly group found effects of both age of acquisition and name agreement on naming accuracy after 5 and 15 s and an effect of word length after 5 but not 15 s. There were no independent effects of picture complexity, object familiarity, word frequency, or imageability. The majority of the elderly subjects' naming errors were semantic in nature, with circumlocutions, visual errors, and "don't know" responses accounting for most of the remaining errors. The implications of the findings for our understanding of word-finding problems in the elderly are discussed.

Real age-of-acquisition effects in lexical retrieval.

Previous research on the effects of age of acquisition on lexical processing has relied on adult estimates of the age at which children learn words. The authors report 2 experiments in which effects of age of acquisition on lexical retrieval are demonstrated using real age-of-acquisition norms. In Experiment 1, real age of acquisition emerged as a powerful predictor of adult object-naming speed. There were also significant effects of visual complexity, word frequency, and name agreement. Similar results were obtained in reanalyses of data from 2 other studies of object naming. In Experiment 2, real age of acquisition affected immediate but not delayed object-naming speed. The authors conclude that age-of-acquisition effects are real and suggest that age of acquisition influences the speed with which spoken word forms can be retrieved from the phonological lexicon.

Cognitive dysfunction in patients treated for pituitary tumours.

Assessment of neuropsychological status and mood was carried out on 36 patients who had been treated for pituitary tumour and on 36 healthy controls. Impairments in memory and executive function were exhibited by the patients even when other known causes of cognitive dysfunction had been excluded. There was no difference in mood between the two groups, and the deficits in cognitive dysfunction were not related to mood disturbance or to the effects of radiotherapy. The defects were however, related to the presence of surgery, although not to the type of surgery. Reasons for the cognitive dysfunction are unclear but are likely to be multifactorial possibly including the effects of neurosurgery and/or hormone imbalance resulting from pituitary surgery.