Using phytoplankton and flow cytometry to analyze grazing by marine organisms

Phytoplankton can, through their autofluorescent characteristics, be thought of as tracer particles in much the same way as fluorescent microspheres when used in particle uptake experiments. Flow cytometric techniques can be used to differentiate phytoplankton from other suspended particles by the two primary autofluorescing photosynthetic pigments, chlorophyll and phycoerythrin. Based on these characteristics, phytoplankton assemblages have been used to assess grazing rates, particle selectivity, and endocytotic abilities in various marine species, from single-celled organisms to higher invertebrates.

Individual differences in cognitive strategy and personality traits as measured by the Sixteen Personality Factor Questionnaire

The relationship between personality and preference for use of the right or left hemisphere of the brain in cognitive processing was investigated. Lateral eye movements were recorded as 50 female and 20 male right-handed subjects considered questions requiring reflection. The questions were not obviously "verbal" or "spatial" in nature but did require differing levels of reflection. Questions requiring higher levels of reflection produced a higher rate of lateral eye movement responses. Percent right eye movement for individual subjects was then correlated with scores on the Sixteen Personality Factor Questionnaire, using both first-order factors and the second-order factor Cortertia, which has some face validity as describing the personality generally ascribed to those who produce mostly right lateral eye movements. No correlation was found between the preferred directions of eye movements and 16 PF factors, which suggests that the lateral eye movements reflect thinking and problem-solving strategies but are not associated with personality styles.

The relationship between auditory sensitivity and ear asymmetry on a dichotic listening task

Using an adaptive forced-choice procedure, the average absolute sensitivity of the right ears of a group of right-handed males was found to be slightly greater than that of their left ears. There was no ear difference in performance on a monaural syllable-identification task using easily detectable stimuli, however. The magnitude of the ear difference in absolute sensitivity was significantly correlated with performance on a dichotic-listening task. In a second experiment, the adaptive forced-choice procedure was used to assess differences in absolute sensitivity in a group of left-handed males. The right ears of those left-handers showing a right-ear advantage on the dichotic-listening task were slightly more sensitive than their left ears. The left ears of those left-handers showing a dichotic left-ear advantage were slightly, but not significantly, more sensitive than their right ears. The correlation of the ear differences in absolute sensitivity with performance on the dichotic-listening task for the left-handers was not significantly different from zero. Results of both experiments are discussed in terms of their implications for the nature of hemispheric asymmetry of function, and the interpretation of dichotic and monaural asymmetries.

Judgments of emotion in words and faces: ERP correlates

Visual event-related potentials (ERPs) to two types of stimuli (faces and words) were analyzed to determine the effects of the perceived emotional connotations of the stimuli (positive, neutral, or negative) in 10 right-handed normal functioning adult males. Principal component analysis (PCA) of the ERPs reveals 5 factors accounting for over 90% of the ERP waveform variance for both faces and words. In the facial data, two ERP components varied in amplitude according to the perceived emotional connotation of the stimulus. For the P3 component, neutrally rated stimuli produced significantly larger amplitudes than stimuli rated as positive or negative. This effect was lateralized to the left hemisphere. A later positive component, the slow wave (448-616 ms), manifested complementary effects, i.e. faces perceived as positive and negative produced larger amplitudes than those perceived as neutral over the right hemisphere. The verbal stimuli did not result in significant main effects for perceived emotional connotation, but produced subtle connotation-related differences in slow wave topography. Hemispheric asymmetries, unrelated to affective connotation, were evident in the verbal data, manifesting different patterns of lateralization depending on the ERP component. The results suggest that differential processing of emotional connotation affects ERP waveforms and that the effects can be understood in terms of ERP components known to be associated with more general aspects of cognitive processing.

Neural temporal coding of low pitch. I. Human frequency-following responses to complex tones

The neural basis of low pitch was investigated in the present study by recording a brainstem potential from the scalp of human subjects during presentation of complex tones which evoke a variable sensation of pitch. The potential recorded, the frequency-following response (FFR), reflects the temporal discharge activity of auditory neurons in the upper brainstem pathway. It was used as an index of neural periodicity in order to determine the extent to which the low pitch of complex tones is encoded in the temporal discharge activity of auditory brainstem neurons. A tone composed of harmonics of a common fundamental produces a sensation of pitch equal to that of the 'missing' fundamental. Such signals generate brainstem potentials which are spectrally similar to FFR recorded in response to sinusoidal signals equal in frequency to the missing fundamental. Both types of signals generate FFR which are periodic, with a frequency similar to the perceived pitch of the stimuli. It is shown that the FFR to the missing fundamental is not the result of a distortion product by recording FFR to a complex signal in the presence of low-frequency bandpass noise. Neither is the FFR the result of neural synchronization to the waveform envelope modulation pattern. This was determined by recording FFR to inharmonic and quasi-frequency-modulated signals. It was also determined that the 'existence region' for FFR to the missing fundamental lies below 2 kHz and that the most favorable spectral region for FFR to complex tones is between 0.5 and 1.0 kHz. These results are consistent with the hypothesis that far-field-recorded FFR does reflect neural activity germane to the processing of low pitch and that such pitch-relevant activity is based on the temporal discharge patterns of neurons in the upper auditory brainstem pathway.

Electrophysiological indices of CNS function in hemodialysis and CAPD

Fourteen Center hemodialysis (CHD) patients, 13 continuous ambulatory peritoneal dialysis (CAPD) patients, and 10 normals matched by group for age and sex were compared using a battery of evoked (EP) and event-related (ERP) brain potential measures to determine the effects on central nervous system (CNS) functioning of these two dialysis modes. While some differences were observed in early brainstem EP waves, the majority of differences occurred in the later waves associated with higher levels of cognitive processing. With tasks involving easy discriminations, CHD patients had longer latencies, indicative of less efficient cognitive processing, than CAPD patients who resembled controls. With difficult tasks, both CHD and CAPD groups showed abnormally-delayed later components. Similar results were obtained for the amplitude of the middle latency N1-P2 component, that is, reduced amplitudes for the CHD group with respect to both CAPD and control groups under low task demand, while both dialysis groups had reduced amplitudes under high task demand. These results suggest that CAPD patients are more similar to normals than CHD patients in ERP indices of attention and the efficiency of cognitive processing.

Event-related potential changes during hemodialysis

Uremia has been associated with a number of neuro-behavioral deficits. In this study, long-latency event-related potentials (ERP's) and the Symbol Digit Modalities Test (SDMT) were used to assess changes in cortical function due to dialysis treatment. Ten chronic renal failure patients, maintained on hemodialysis, were tested. ERP and SDMT measures were taken immediately before and after dialysis. As a control for any practice effects or neurocognitive changes not associated with hemodialysis, the patients were also assessed with the same procedures on a day off dialysis. Significant increases in N2 and P3 amplitude were demonstrated following the dialysis treatment suggesting that a routine hemodialysis treatment increases the intensity of neural activation. Speed of cortical function, as indexed by ERP component latency and the SDMT, was not affected in any consistent manner by dialysis. However, changes during dialysis in the latency of late ERP components were correlated with changes in subject's serum electrolyte levels, indicating that the speed of cortical function is related to blood electrolyte levels. Differences between subjects in the pre-dialysis latency of the P3 component of the ERP was correlated with pre-dialysis levels of calcium and uric acid, as well as with performance on the SDMT.

Event-related potential concomitants of information processing dysfunction in schizophrenic children

ERPs were recorded from 10 schizophrenic and 13 normal children during the performance of the Span of Apprehension task (Span). This task involves the discrimination of a randomly placed target letter among distractors, and it has been shown to discriminate between normal and schizophrenic individuals. The EEG was recorded at 7 scalp loci, and ERPs were averaged over a 1500 msec interval initiated by a warning tone which preceded the visual Span stimuli by 500 msec. Stimulus arrays were grouped into 4 levels of difficulty. The data from both subject groups were combined in a single principal components analysis (separate PCAs exhibited few differences between groups) generating 8 rotated factors which were readily interpreted in terms of conventional ERP components. Factor scores for the two groups were examined using Analysis of Variance. The schizophrenic children produced a small CNV which was slow to develop and resolve as well as diminished amplitudes for the N1, P3 and slow wave components. This suggests that these children are impaired in their ability to regulate processes involved in the mobilization and direction of attention and the discrimination of target stimuli. Significantly, the schizophrenic children did not show progressive increases in N1 and SW amplitudes in response to increases in information processing demand (array difficulty) as was the case in the normal children. ERP components of the schizophrenic children were most aberrant at frontal leads, but midline and lateralized deficits were also seen at vertex and posterior recording sites.

Laterality effects in response to the offset of visual stimuli

In a study of simple reaction time to visual stimuli it was found that the offset (or termination) of stimuli presented in the right visual field elicits significantly later responses than does the offset of stimuli presented in the left visual field. No such difference was observed for the responses to stimulus onset. A similar effect has been reported for responses to tonal stimuli. The results do not support the view that hemispheric asymmetries arise at higher stages of information processing than those which mediate simple reaction time.

Frequency discrimination and signal detection in band-reject noise

An experiment was conducted in order to compare the importance of information from frequency regions remote from the nominal signal frequencies for frequency discrimination and signal detection. In both tasks, signals were presented within the "notch" of band-reject noise, and different notch widths were employed. The results indicate that information is integrated over a wider range in frequency discrimination than in signal detection. Further, experiments in which a noise floor was present as well as band-reject noise, indicate that disrupting the information from regions remote from the nominal signal frequencies impairs frequency discrimination even in the absence of any significant impairment of signal detection performance.

Exponential electrophysiological aging: P3 latency

Forty-nine normal volunteer subjects ranging in age from 15 to 80 years were studied in an 'auditory oddball' event-related potential paradigm. In certain respects our results replicate other studies, finding significant correlations between age and both N2 and P3 latency. Slopes of the linear age/ERP latency regression function increased with component number (i.e., N1 less than P2 less than N2 less than P3). Further analysis disclosed that the age/ERP component latency relationship is non-linear. Separate age/ERP component latency linear regression functions were computed for subjects 15-45 and 46-80. None of these functions were significant for subjects under 45. Age/latency slopes were significant in the older group for P2, N2 and P3. The age/P3 latency slope for the subjects under 45 was 0.53 msec/year, versus 3.14 msec/year for the subjects over 45. The data for P3 latency and age are best fitted with a curvilinear first and second degree orthogonal polynomial, which describes a positively accelerating latency increase with age. Clinical implications of the form of the age/P3 latency regression function (curvilinear vs. linear) are discussed.

Effects of utterance position on English speech timing

8 speakers of American English produced utterances consisting of one to five disyllables ([bábe] or [pápe]). Vowel and stop closure intervals were defined by variations in supraglottal pressure, sensed through a thin tube inserted in the mouth. Closure was always longer for /p/ than /b/ in utterance-medial positions. In utterance-initial position, however, /b/ lengthened more than /p/ so that no duration difference between /p/ and /b/ was observed. Utterance-initial position did not influence vowel duration. In contrast, utterance-final position affected only vowel duration, lengthening both final-syllable unstressed vowels and stressed vowels in penultimate syllables.

Vocal register "shift" identification in a modified breathing atmosphere

An attempt was made to determine whether listeners' perception of vocal register "shift" was related to speaker fundamental frequency or to supralaryngeal resonance. The method was to have speakers phonate tones while breathing air and, alternatively, a helium--oxygen mixture which influences resonance but not fundamental frequency. Recordings were made of these phonations and played to judges who were required to identify between which tones the register shift occurred. Results showed that judges had more difficulty identifying the shift point when speakers were phonating in air than with the HeO2 mixture. Comparison also was made between the speaker's self-judgment of shift and that of listeners. Under the helium condition the speakers and listeners were in nearly complete agreement, with the greatest variability occurring between the groups for the air breathing condition. These results indicate that register change is related to modification of laryngeal function.

Principal component analysis of ERP differences related to the meaning of an ambiguous word

Event-related potentials (ERPs) to the noun and verb meanings of/'led/in the single ambiguous phrase 'it was/'led/' were re-analyzed using principal component analysis (PCA). These data had previously been analyzed by SWDA and reported in this journal. PCA defined 3 meaning-related components, comprising 40.3% of the entire data variance. The N150 component was shown to be larger for the noun meaning than for the verb meaning; the P230 epoch differed in its anterior-posterior distribution according to meaning; and N370 for noun responses was relatively more negative at the right posterior lead and positive at the left anterior. All components taken together, the left anterior lead showed the greatest meaning-related difference. Previous analysis by SWDA had resulted in significant discriminant functions for left hemisphere ERPs, but this analysis did not yield a clear definition of the effects of meaning on specific ERP components or of the scalp distributions of meaning-related components. Thus, while the results of both analyses support the interpretation that the perceived meaning of words has a substantial effect on ERP wave forms, PCA appears to provide the clearest definition of the ERP component effects.

Human auditory frequency-following responses to a missing fundamental

Both a complex tone perceived as a 365-hertz "missing fundamental" and a 365-hertz pure tone evoked 365-hertz far-field frequency-following responses. Narrow-band masking noise centered at 365 hertz attenuated the responses to the pure tone but not to the complex tone. Results support the concept that perception of the missing fundamental is based on periodic neural activity.

Effect of cooling techniques on temperature control and cutting rate for high-speed dental drills

This paper describes a series of tests conducted to determine the effectiveness of various cooling techniques used while preparing teeth for restoration. Comparisons are presented for four cooling techniques: air stream, air-water spray, water stream from a separate hand-held syringe, and water applied through a hollow bur. The comparisons were made in two ways, temperature control and influence on cutting rate. It was demonstrated that wet cooling techniques provided better temperature control than cooling with air and also improved the rate of material removal.

Thermal stress in teeth

Observations of crack damage in the tooth structure from in vivo studies and in vitro experimental thermal cycling studies were combined with numerical analysis techniques to identify and isolate the influence of thermal stresses on the creation and propagation of cracks in teeth. The factors considered in this study included: (a) variations in tooth type or geometry (molar, bicuspid, etc.), (b) tooth age, (c) material properties of the tooth, (d) the magnitude of the change in the temperature of the environment surrounding the tooth, and (e) the thermal resistance between the tooth and the medium surrounding the tooth.

Numerical and experimental evaluation of energy inputs, temperature gradients, and thermal stresses during restorative procedures

Wet cutting in enamel should be used during restorative procedures. According to evidence reported here, dry cutting can induce sufficiently high thermal stresses to fracture the enamel. Temperatures resulting from dry cutting in dentin are high enough to cause biologic pulp damage if the cutting is within 1 to 2 mm of the pulp. Cracks induced in the cavity walls by dry cutting may eventually contribute to marginal failure. A hand-held syringe directing a small, high-velocity stream of water into the cutting region is a more effective cooling technique than an air-water spray.

Communicating with hearing-impaired patients

ONE ASPECT OF ESTABLISHING EFFECTIVE COMMUNICATION BETWEEN PHYSICIANS AND PATIENTS HAS NOT RECEIVED ADEQUATE ATTENTION: the special needs and challenges presented by patients with impaired hearing. In this article the term "hearing impaired" is generic and is applied to both those persons who are commonly labeled "deaf" and those labeled "hard of hearing" as a result of a bilateral hearing loss. The general skills, both verbal and nonverbal, that a physician must have in order to communicate successfully with a hearing-impaired patient are in essence the same as those required for a hearing patient. Where the divergence occurs is not in the basic skills (empathy, probing and the like) but rather in the means of applying them. Communicating with a hearing-impaired patient makes the use of some combination of the following necessary: speech, hearing, speechreading (lipreading), writing, visual aids, visual language systems and the assistance of an interpreter.

Evoked potential waveform differences produced by the perception of different meanings of an ambiguous phrase

To test the effects of perceived linguistic meaning on evoked potential (EP) waveform, an experiment was performed using the stimulus homophone "led" or "lead" in the single ambiguous phrase "it was /'led/". The phrase was presented aurally in sets of 60 repetitions, instructing the subject before each set as to the specific meaning of the stimulus word to be perceived. Averages of one hundred responses were obtained for each of the two meanings of the stimulus. Responses were recorded from scalp locations over Broca's and Wernicke's areas and homologous right hemisphere loci. Average waveforms evoked by the two meanings of the stimulus word were dissimilar for the left anterior locus and similar for the other three loci as indicated by correlations. The application of the Discrimination Index to these data disclosed that the EP waveform differences observed at the left anterior locus would not be attributed to random variability. Stepwise Discriminant Function Analysis on the same data revealed that responses from individual subjects could be classified according to experimental conditions at a greater-than-chance level. Discrimination was best for responses from left hemisphere loci. There was some commonality of discriminative EP components across subjects, specifically components late in the EP epoch. These data are interpreted as demonstrating an EP correlate of the processing of the contextual meaning of words.

Far-field recorded frequency-following responses: evidence for the locus of brainstem sources

Two experiments were performed to determine the brainstem origins of the scalp recorded auditory frequency-following response (FFR). The first was a study of FFR onset latency in which responses observed by direct recording from depth electrodes in brainstem auditory nuclei were compared with those obtained from the scalp. The mean onset latency of scalp recorded FFR (5.8 msec) closely approximated the 5.4 msec mean latency of response recorded from within the inferior colliculus (IC). In a second experiment, cooling of the IC greatly reduced or eliminated FFR both within this nucleus and at the scalp. FFR at the medial superior olive was unaffected during cooling. It was concluded that at moderate intensities of stimulation the primary source of scalp recorded FFR is the IC.

Far-field recorded frequency-following responses: correlates of low pitch auditory perception in humans

The recent demonstration that auditory frequency-following responses (FFR) can be recorded by signal averaging from the human scalp, opened the way for studies correlating FFR with auditory experience. This report describes FFR amplitude changes as a function of stimulus intensity and the addition of masking noise. The first experiment revealed a high degree of consistency both within and across subjects in the latency, phase and waveform of averaged FFR. This experiment also demonstrated a monotonic relationship between average FFR amplitude and stimulus intensity between 40 and 65 dB SL. Results of the second experiment showed a close correlation between the detectability of a tone in a noise masker and FFR amplitude. FFR amplitude diminishes precipitously as noise intensity approaches or exceeds the threshold for masking of the tone. These results are interpreted as emphasizing the role of neural periodicity mechanisms in the preception of low frequencies.

Relationship of lingual and intraoral air pressures during syllable production

The production of many consonant sounds requires a buildup of air pressure within die oral cavity. This buildup often results from resistance to air flow created in the vocal tract by tongue movements. This study investigated the relationship of tongue pressure to intraoral air pressure. Four male speakers repeated VCV syllables containing /t/, /d/, and /n/ combined with /i/, /α/, and /u/. Each combination was repeated at a constant rate at three intensity levels. Air-pressure variations associated with the consonants were recorded from the oral-pharyngeal region while tongue pressures were recorded from behind the maxillary central incisors and above the left and right maxillary molars. The results show that for stop-consonant production, air pressures and lateral tongue pressures vary in parallel manner, whereas tongue tip pressures appear to act independently of both air and side tongue pressures. Vocal intensity changes are an exception to this in that both intraoral air and tongue pressures increased as intensity increased, the greatest change occurring for tongue tip pressures.

Heat transfer in teeth

Experiments were conducted to determine the thermal resistance between food and teeth during mastication processes and the drinking of beverages. It was found that the assumption of negligible resistance between food and teeth overestimates greatly the resulting temperature gradients. Also, heat transfer coefficients (reciprocal thermal resistance) during drinking and mastication are below 7.0 X 10 -2 calorie/cm2 second°C.

Thermal fatigue in teeth

This paper presents the results of experiments conducted with extracted human and bovine teeth. The teeth were subjected to thermal cycling at temperatures between 140 and 90 F. The results offer conclusive evidence that thermal fracture may be induced by the thermal stresses caused by the temperature cycling. Less than 3,000 thermal cycles cause severe cracking or the propagation of cracks previously existing in the teeth, or both.

Thermal properties of teeth

Recent measurements of the density and specific heat of teeth, as well as values of thermal di ff usivity based on thermal conductivity measurements, are reported. The values obtained for thermal di~usivity were within 10% (for enamel) and 25% (for dentin) of values previously reported in the literature.