An Easy-to-Construct Automated Winkler Titration System

The instrument described in this report is an updated version of the high precision, automated Winkler titration system described by Friederich et al.(1984). The original instrument was based on the work of Bryan et al. (1976) who developed a colorimetric endpoint detector and on the work of Williams and Jenkinson (1982) who produced an automated system that used this detector. The goals of our updated version of the device described by Friederich et al. (1984) were as follows: 1) Move control of the system to the MS-DOS environment because HP-85 computers are no longer in production and because more user-friendly programs could be written using the IBM XT or AT computers that control the new device. 2) Use more "off the shelf" components and reduce the parts count in the new system so that it could be easily constructed and maintained. This report describes how to construct and use the new automated Winkler titration device. It also includes information on the chemistry of the Winkler titration, and detailed instructions on how to prepare reagents, collect samples, standardize and perform the titrations (Appendix I: Codispoti, L.A. 1991 On the determination of dissolved oxygen in sea water, 15pp.). A disk containing the program needed to operate the new device is also included. (pdf contains 33 pages

Alpha-band oscillations and emotion: A review of studies on picture perception

Although alpha-band activity has long been a focus of psychophysiological research, its modulation by emotional value during picture perception has only recently been studied systematically. Here, we review these studies and report that the most consistent alpha oscillatory pattern indexing emotional processing is an enhanced desynchronization (ERD) over posterior sensors when viewing emotional compared with neutral pictures. This enhanced alpha ERD is not specific to unpleasant picture content, as previously proposed for other measures of affective response, but has also been observed for pleasant stimuli. Evidence suggests that this effect is not confined to the alpha band but that it also involves a desynchronization of the lower beta frequencies (8-20 Hz). The emotional modulation of alpha ERD occurs even after massive stimulus repetition and when emotional cues serve as task-irrelevant distractors, consistent with the hypothesis that evaluative processes are mandatory in emotional picture processing. A similar enhanced ERD has been observed for other significant cues (e.g., conditioned aversive stimuli, or in anticipation of a potential threat), suggesting that it reflects cortical excitability associated with the engagement of the motivational systems

Visual-cortical enhancement by acoustic distractors: The effects of endogenous spatial attention and visual working memory load

Past work has shown that when a peripheral sound captures our attention, it activates the contralateral visual cortex as revealed by an event-related potential component labelled the auditory-evoked contralateral occipital positivity (ACOP). This cross-modal activation of the visual cortex has been observed even when the sounds were not relevant to the ongoing task (visual or auditory), suggesting that peripheral sounds automatically activate the visual cortex. However, it is unclear whether top-down factors such as visual working memory (VWM) load and endogenous attention, which modulate the impact of task-irrelevant information, may modulate this spatially-specific component. Here, we asked participants to perform a lateralized VWM task (change detection), whose performance is supported by both endogenous spatial attention and VWM storage. A peripheral sound that was unrelated to the ongoing task was delivered during the retention interval. The amplitude of sound-elicited ACOP was analyzed as a function of the spatial correspondence with the cued hemifield, and of the memory array set-size. The typical ACOP modulation was observed over parieto-occipital sites in the 280–500 ms time window after sound onset. Its amplitude was not affected by VWM load but was modulated when the location of the sound did not correspond to the hemifield (right or left) that was cued for the change detection task. Our results suggest that sound-elicited activation of visual cortices, as reflected in the ACOP modulation, is unaffected by visual working memory load. However, endogenous spatial attention affects the ACOP, challenging the hypothesis that it reflects an automatic process

Modulation of early ERPs by accurate categorization of objects in scenes

The categorization of objects within natural scenes is carried out in a sequence of stages, which may build on the detection of perceptual regularities in the visual appearance of objects or may represent a more semantic level of categorization. Here, we examined the neural correlates of correct categorization of objects in scenes, using natural scenes which were equalized in color and spectral amplitude, and controlled in terms of spatial coherence. Event-related potentials (ERPs) were used to track the early stages of visual processing. Participants viewed degraded (phase-scrambled) versions of natural scenes and then categorized them as depicting animals or people. At an intermediate scrambling level, a negative-going occipitotemporal ERP modulation by categorization accuracy was observed, beginning approximately 150 ms after stimulus onset; at more degraded levels, no ERP modulation was observed. These results suggest that this early negative-going ERP modulation reflects processing of perceptual evidence which is predictive of later correct categorization, even when low-level differences in color, spectral amplitude, and spatial coherence are balanced or controlled

Novelty and learning in cognitive control: evidence from the Simon task

While information that is associated with inappropriate responses can interfere with an ongoing task and be detrimental to performance, cognitive control mechanisms and specific contextual conditions can alleviate interference from unwanted information. In the spatial correspondence (Simon) task, interference has been consistently shown to be reduced by spatial non-correspondence in the previous trial (i.e., correspondence sequence effect, CSE); however the mechanisms supporting this sequential effect are not well understood. Here we investigated the role of novelty and trial-to-trial changes in stimulus and response features in a Simon task, observing similar modulation of CSE for novel and non-novel stimulus changes. However, changing the response modality from trial to trial dampened CSE, and this dampening was more pronounced when the probability of switch trials was higher, suggesting a role for long-term learning. The results are consistent with recent accounts, which indicate that spatial interference can be prevented by cognitive control mechanisms triggered by learned bindings

Effects of Picture Size Reduction and Blurring on Emotional Engagement

The activity of basic motivational systems is reflected in emotional responses to arousing stimuli, such as natural pictures. The manipulation of picture properties such as size or detail allows for investigation into the extent to which separate emotional reactions are similarly modulated by perceptual changes, or, rather, may subserve different functions. Pursuing this line of research, the present study examined the effects of two types of perceptual degradation, namely picture size reduction and blurring, on emotional responses. Both manipulations reduced picture relevance and dampened affective modulation of skin conductance, possibly because of a reduced action preparation in response to degraded or remote pictures. However, the affective modulation of the startle reflex did not vary with picture degradation, suggesting that the identification of these degraded affective cues activated the neural circuits mediating appetitive or defensive motivation

The Potential for Using Little Diomede Island as a Platform for Observing Environmental Conditions in Bering Strait

The Pacific waters that enter the Arctic via the Bering Strait exert a major influence on the Arctic Ocean’s stratification, ice cover, and ecosystem. We demonstrate the potential of a shore-based laboratory to monitor the water masses that flow predominantly northward past Little Diomede Island in the center of the Bering Strait into the Arctic Ocean. We determined near-surface water column salinity, inorganic nutrient concentrations, natural fluorescence associated with chlorophyll, and the oxygen isotope composition of seawater, both in summer during the open-water period and in late winter under ice-covered conditions, by pumping ashore water from shallow depths near the island. Additional surveys were undertaken within 5 km of the island to assess the influence of local sources of nutrients. Water mass variability was much greater during the open-water period than under ice-covered conditions, presumably because the relatively immobile ice cover attenuates wind forcing and the decrease in run-off reduces cross-shelf gradients. The mean oxygen isotope composition of the summer (?18O = -1.11‰) and late winter (?18O = -0.98) collections, however, was close to that which has been established for Bering Sea waters in the Pacific-dominated upper halocline of the Arctic Ocean (-1.1‰) particularly considering the higher seasonal flow of runoff in the summer. A comparison with data from shipboard sampling at various locations across the Bering Strait indicates that the oxygen isotope composition of near-surface water sampled at Diomede varies in response to wind-forcing. If the least saline (< 30.5) water near the Alaska coast is excluded, the ?18O values of Diomede and shipboard samples cannot be distinguished statistically. This similarity suggests that the water sampled from the island also reasonably represents the ?18O value of Bering Sea waters that contribute to the upper halocline of the Arctic Ocean. Effects of benthic recycling, human activity, and seabird nesting on nutrient concentrations appeared to be concentrated within ~200 m of the island. Our results are discussed in the practical context of availability of electricity, interested local residents, and a geotechnical study indicating that it is feasible to construct and operate a more permanent undersea water intake system to improve environmental observation capabilities in the Bering Strait region.Les eaux du Pacifique qui entrent dans l’Arctique par le détroit de Béring ont une influence majeure sur la stratification, le couvert de glace et l’écosystème de l’océan Arctique. Dans ce rapport nous présentons des données qui démontrent le potentiel d’un laboratoire basé à terre dans le but de surveiller les masses d’eau qui circulent principalement vers le nord au-delà de l’île Little Diomede au centre du détroit de Béring jusqu’à l’océan Arctique. Nous avons déterminé la salinité de la colonne d’eau près de la surface, la concentration des nutriments inorganiques, la fluorescence naturelle associée avec la chlorophylle, ainsi que la composition en isotope d’oxygène de l’eau de mer. Ces données ont été recueillies pendant la période estivale en eaux ouvertes et à la fin de l’hiver sous des conditions de couvert de glace en pompant à terre l’eau provenant d’aires peu profondes près de l’île. Des études supplémentaires ont été entreprises à moins de 5 km de l’île afin d’évaluer l’influence des sources locales de nutriments. La variabilité des masses d’eaux était plus grande pendant la période sans couvert de glace que pendant les conditions de couvert de glace. Ceci était vraisemblablement dû à l’atténuation de la force exercée par le vent sous le couvert de glace relativement immobile et à une réduction des gradients à travers le plateau provenant d’une réduction du ruissellement. La composition moyenne en isotope d’oxygène des collections de l’été (?18O = -1.11‰) et de fin d’hiver (?18O = -0.98‰) étaient cependant près de celle qui a été établie pour les eaux de la mer de Béring dans l’halocline supérieure de l’océan Arctique dominée par les eaux du Pacifique (?18O = -1.1‰), particulièrement compte tenu du flux saisonnier de ruissellement plus élevé pendant l’été. Une comparaison avec des données recueillies par bateau à plusieurs locations à travers le détroit de Béring indique que la composition en isotope d’oxygène près de la surface des eaux mesurée à Diomede varie en réponse à la force du vent. Lorsque l’eau moins saline (< 30.5) près de la côte de l’Alaska est exclue, les valeurs ?18O de Diomede et des échantillons recueillis par bateau ne peuvent être distingués statistiquement. Cette similarité suggère que l’eau échantillonnée à partir de l’île représente aussi raisonnablement les valeurs ?18O des eaux de la mer de Béring qui contribuent à l’halocline supérieure de l’océan Arctique. Les conséquences du recyclage benthique, des activités anthropogéniques et de la nidification des oiseaux de mer sur les concentrations de nutriments semblent être concentrées à moins de ~200m de l’île. Nos résultats sont interprétés dans le contexte pratique de la disponibilité de l’électricité, de l’intérêt des résidents locaux et d’une étude géotechnique qui indique qu’un système permanent de prise d’eau sous-marin peut être construit et opéré afin d’améliorer les capacités d’observation environnementale dans la région du détroit de Béring