Auditory cortical responses in the cat to sounds that produce spatial illusions

Humans and cats can localize a sound source accurately if its spectrum is fairly broad and flat(1-3), as is typical of most natural sounds. However, if sounds are filtered to reduce the width of the spectrum, they result:in illusions of sources that are very different from the actual locations, particularly in the up/down and front/back dimensions(4-6). Such illusions reveal that the auditory system relies on specific characteristics of sound spectra to obtain cues for localization(7). In the-auditory cortex of cats, temporal firing patterns of neurons can signal the locations of broad-band sounds(8-9). Here we show that such spike patterns systematically mislocalize sounds that have been passed through a narrow-band filter. Both correct and incorrect locations signalled by neurons can be predicted quantitatively by a model of spectral processing that also predicts correct and incorrect localization judgements by human listeners(6). Similar cortical mechanisms, if present in humans, could underlie human auditory spatial perception.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62778/1/399688a0.pd

The Effects of Childhood Stress on Health Across the Lifespan

Stress is an inevitable part of life. Human beings experience stress early, even before they are born. A certain amount of stress is normal and neces-sary for survival. Stress helps children develop the skills they need to cope with and adapt to new and potentially threatening situations throughout life. Support from parents and/or other concerned caregivers is necessary for children to learn how to respond to stress in a physically and emotion-ally healthy manner.The beneficial aspects of stress diminish when it is severe enough to over-whelm a child’s ability to cope effectively. Intensive and prolonged stress can lead to a variety of short- and long-term negative health effects. It can disrupt early brain development and compromise functioning of the nervous and immune systems. In addition, childhood stress can lead to health problems later in life including alcoholism, depression, eating disorders, heart disease, cancer, and other chronic diseases.The purpose of this publication is to summarize the research on childhood stress and its implications for adult health and well-being

Location Coding by Opponent Neural Populations in the Auditory Cortex

Although the auditory cortex plays a necessary role in sound localization, physiological investigations in the cortex reveal inhomogeneous sampling of auditory space that is difficult to reconcile with localization behavior under the assumption of local spatial coding. Most neurons respond maximally to sounds located far to the left or right side, with few neurons tuned to the frontal midline. Paradoxically, psychophysical studies show optimal spatial acuity across the frontal midline. In this paper, we revisit the problem of inhomogeneous spatial sampling in three fields of cat auditory cortex. In each field, we confirm that neural responses tend to be greatest for lateral positions, but show the greatest modulation for near-midline source locations. Moreover, identification of source locations based on cortical responses shows sharp discrimination of left from right but relatively inaccurate discrimination of locations within each half of space. Motivated by these findings, we explore an opponent-process theory in which sound-source locations are represented by differences in the activity of two broadly tuned channels formed by contra- and ipsilaterally preferring neurons. Finally, we demonstrate a simple model, based on spike-count differences across cortical populations, that provides bias-free, level-invariant localization—and thus also a solution to the “binding problem” of associating spatial information with other nonspatial attributes of sounds

Effects of Temperature on the Toxicity of Oil Refinery Waste, Sodium Chlorate, and Treated Sewage to Fathead Minnows

A literature review and experiments were conducted to determine the effects of temperature on the toxicity of three materials to fish (fathead minnows

The Effect of Carbon on Algal Growth--Its Relationship to Eutrophication

Introduction: Natural and cultural eutrophication (enrichment with nutrients) frequnetly results in excessive algal growths thereby reducing the beneficial uses of surface waters (Hasler, 1947; Thomas, 1955, Edmondson et al., 1956, Oswald and Golueke, 1966, Skulberg, 1967, Mackenthun et al., 1968, Goldman and Armstrong, 1969, McGauhey et al., 1968,1969, 1970a, 1970b). Recent reviews emphsize that the prevention of further reduction in the quality of water resources requires the implementation of effective control measures (Goldman, 1965, Steward and Rohlich, 1967, Middlebrooks et al., 1969, Rohlich, 1969). Effective control of cultural eutrophication must involve the manipulation of those factors which affect algal growth, i.e. light, temperature, nutrients, mixing predation, etc. (Toerien et al., 1970). Because at the present time man can only effectively control the discharge of nutrient concentrations into aquatic systems, most past and current research on the remediation of eutrophication effects has been concerned with nutrient control. The cost of removal (or exclusion) of specific nutrients varies, so from an economic standpoint it becomes important to indentify which nutrients limit algal growth for a given situation. Algae require carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, magnesium, iron, potassium, various other cations, and anumber of trace elemtns to carry out the metabolic processes necessary for growth. Only a few of these elements can be removed from water through treatment at this time. Althrough Goldman (1960) and Skulberg (1967) have implicated magnesium, iron and molybdenum, and other trace elements as limiting factors for algal growth in some waters, most attention has been directed towards nitrogen and phosphorus as limiting nutrients. Several reasons for this interst in nitrogen and phosphorus follow: (1) Nitrogen and phosphorus are relatively major constitutents in algae; a typical stoichiometric formula for algal biomass being C106H181O45N16P (McCarty, 1970); (2) Geochemical considerations suggest that phosphorus is probably the most frequently limiting nutrient (Hutchinson, 1957); (3) The considerably detailed information on the behavior of nitrogen and phosphorus in nature (Hutchinson, 1957, Task Group 2610P (AWWA), 1967); (4) The relative ease and familiarity of chemical analysis (e.g. Amer. Publ. Health Assoc., 1965) at the relatively high concentraions observed in waste waters (McGauhey, 1968); (5) the vast amount of research performed on the physiological and biochemical utilization of nitrogen and phosphorus (e.g. Fogg, 1959, Lewin, 1962, Kuh, 1968); (6) at least for phosphorus, the relative ease with which it can be removed from waste waters by chemical treatment (Wuhrmann, 1957, Rohlich, 1961). Because phosphorus can be removed relatively easily in both economical and technical terms (e.g. Cult and Moyer, 1969) and because it has been considered to be the most probable limiting nutrient in most natural waters, proposals for constructin tertiary treatment plants for removing phosphorus from waste waters, elimination of phosphate builders in detergents, and limitations on the use of phosphorus fertilizers have been advanced as aids in controlling eutrophication. Recently the concept that phosphorus is the most probable limiting nutrient in natural waters habeen questioned (Legge and Dingledein, 1970) and several investigators have suggested that carbon is really the most important limitng nutrient in natural waters (lange, 1067, Kuentzel, 1969, Kerr et al., 1970, King, 1971). These considerations have now entered the realm of controversy (Kuentzel, 1969, 1970, Legge and Dingledein, 1970, Sawyer, 1970, Shapiro, 1970, Abelson, 1970, Bowen, 1970, Likens, 1971). The implication of carbon as being a major factor in controlling cultural eutrophication has significant consequences. Currently removal of phophorus from detergents has been advocated (Environmental Science and Technology, 1970, Dawson, 1970). The economic aspects of phosphoros removal and replacement with other materials for the consumer and manufacturer and the environmental effects of possible replacements (e.g. substitutes similar to the recently banned nitrito-triacetic acid (NTA)) on aquatic ecosystems have not been evaluated. Therefore, serious questioning of the role of phosphorus in the eutrophication of natural waters may be warranted. However, the possible role of other factors which can limit algal populations should be considered in light of the extensive literature which exists on the subject of algal growth. It is the goal of this review to clarify and obtain a perspective on the role of carbon in controlling algal growth in natural waters. information on carbon cycling and metabolism, inorganic carbon chemistry, algal utilization of carbon, and concepts of nutrient limitations will be discussed and reviewed to gain this perspective. This information will provide for a more complete understanding of the role of carbon in eutrophication

V/STOL lift fan commercial short haul transports: Continuing conceptual design study

A design study of commercial V/STOL transport airplanes for a 1985 operational time period has been made. The baseline mission considered was 400 nmi at a cruise speed of M = 0.75 and a 100-passenger payload with VTOL. Variations from the baseline included mission distance, payload, cruise speed, and propulsion system failure philosophy. All designs used propulsion systems consisting of multiple gas generators driving remote tip turbine lift and lift/cruise fans. By considering the fan to be designed for operational reliability, significant simplication of the airplane systems and reduction in airplane size and cost can be achieved

Cortical Responses to Cochlear Implant Stimulation: Channel Interactions

This study examined the interactions between electrical stimuli presented through two channels of a cochlear implant. Experiments were conducted in anesthetized guinea pigs. Multiunit spike activity recorded from the auditory cortex reflected the cumulative effects of electric field interactions in the cochlea as well as any neural interactions along the ascending auditory pathway. The cochlea was stimulated electrically through a 6-electrode intracochlear array. The stimulus on each channel was a single 80- µ s/phase biphasic pulse. Channel interactions were quantified as changes in the thresholds for elevation of cortical spike rates. Experimental parameters were interchannel temporal offset (0 to ±2000 µ s), interelectrode cochlear spacing (1.5 or 2.25 mm), electrode configuration (monopolar, bipolar, or tripolar), and relative polarity between channels (same or inverted). In most conditions, presentation of a subthreshold pulse on one channel reduced the threshold for a pulse on a second channel. Threshold shifts were greatest for simultaneous pulses, but appreciable threshold reductions could persist for temporal offsets up to 640 µ s. Channel interactions varied strongly with electrode configuration: threshold shifts increased in magnitude in the order tripolar, bipolar, monopolar. Channel interactions were greater for closer electrode spacing. The results have implications for design of speech processors for cochlear implants.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41382/1/10162_2003_Article_3057.pd

Distributed coding of sound locations in the auditory cortex

Although the auditory cortex plays an important role in sound localization, that role is not well understood. In this paper, we examine the nature of spatial representation within the auditory cortex, focusing on three questions. First, are sound-source locations encoded by individual sharply tuned neurons or by activity distributed across larger neuronal populations? Second, do temporal features of neural responses carry information about sound-source location? Third, are any fields of the auditory cortex specialized for spatial processing? We present a brief review of recent work relevant to these questions along with the results of our investigations of spatial sensitivity in cat auditory cortex. Together, they strongly suggest that space is represented in a distributed manner, that response timing (notably first-spike latency) is a critical information-bearing feature of cortical responses, and that neurons in various cortical fields differ in both their degree of spatial sensitivity and their manner of spatial coding. The posterior auditory field (PAF), in particular, is well suited for the distributed coding of space and encodes sound-source locations partly by modulations of response latency. Studies of neurons recorded simultaneously from PAF and/or A1 reveal that spatial information can be decoded from the relative spike times of pairs of neurons – particularly when responses are compared between the two fields – thus partially compensating for the absence of an absolute reference to stimulus onset.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47436/1/422_2003_Article_439.pd

Auditory Cortical Images of Tones and Noise Bands

We examined the representation of stimulus center frequencies by the distribution of cortical activity. Recordings were made from the primary auditory cortex (area A1) of ketamine-anesthetized guinea pigs. Cortical images of tones and noise bands were visualized as the simultaneously recorded spike activity of neurons at 16 sites along the tonotopic gradient of cortical frequency representation. The cortical image of a pure tone showed a restricted focus of activity along the tonotopic gradient. As the stimulus frequency was increased, the location of the activation focus shifted from rostral to caudal. When cochlear activation was broadened by increasing the stimulus level or bandwidth, the cortical image broadened. An artificial neural network algorithm was used to quantify the accuracy of center-frequency representation by small populations of cortical neurons. The artificial neural network identified stimulus center frequency based on single-trial spike counts at as few as ten sites. The performance of the artificial neural network under various conditions of stimulus level and bandwidth suggests that the accuracy of representation of center frequency is largely insensitive to changes in the width of cortical images.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41376/1/10162_2000_Article_36.pd