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PubMed2002

High-rate denitrification and SS rejection by biofilm-electrode reactor (BER) combined with microfiltration.

In this study, a multi-cathode biofilm-electrode reactor (BER) combined with microfiltration (MF) was investigated using a laboratory-scale experimental apparatus for treatment of nitrate-contaminated water. The multi-cathode electrodes were composed of multiple-granular activated carbons (GACs). GACs attached to each cathode to enlarge surface area of electrodes and to attach bacteria quickly and firmly. In BER, H2 gas is produced by applying electric current, which serves as an electron donor in biological reduction of nitrate to N2 gas. Since some suspended solids were escaping from BER, MF membrane with plate modules and a pore size of 0.2 microm was placed after BER. Experimental results demonstrated that it was possible to operate the multi-cathode BER with high denitrification rates and hydraulic retention time (HRT) as low as HRT = 20 min. The denitrification rate was enhanced by 3-60 times in comparison with former studies. MF membrane successfully rejected the bacteria escaping from BER, so that the effluent concentration of SS was kept below 1 mg SS/l throughout the experiment. It was also possible to operate MF membrane at flux 2-9 times higher and pressure 2.5-31 times smaller than in former studies. This higher performance was mainly brought about by using biofilm and H2 gas as an electron donor. Also, an economic evaluation of BER/MF was included, showing the feasibility of this process. The present BER/MF process is considered advantageous for the enhanced treatment of nitrate-polluted groundwater.

Biofilms↗
PubMed2001

Characterization of the iontophoretic permselectivity properties of human and pig skin.

The objectives of this research were (a) to characterize the permselective properties of human and porcine skin and (b) to assess the validity of the latter as a model membrane in iontophoresis studies. The electroosmotic transport of [14C]mannitol was followed in vitro across human and porcine skin as a function of pH, in both "anode-to-cathode" and "cathode-to-anode" directions. At physiological pH, mannitol electrotransport dominated in the anode-to-cathode direction, clearly indicating the net negative charge and the corresponding cation-permselectivity of the skin. By lowering the pH to 3.5 the direction of electroosmosis progressively reverses, indicating that the skin is becoming net positively-charged, and thus anion-selective. The degree of permselectivity (DP) of the skin at each pH value was quantified by dividing mannitol electrotransport in the predominant direction (i.e. either anodal or cathodal) by that in the opposite sense. The net charge on the skin is zero when DP equals unity, corresponding to the isoelectric point (pI) of the membrane (approximately 4.4 for pig skin and approximately 4.8 for human skin). The consistent pIs and similar pH-dependent permselectivities observed for human and pig demonstrate that porcine skin is an appropriate model for iontophoresis studies. Finally, the characterization of the permselective properties of human skin is crucial to optimize the iontophoresis of large peptides and uncharged species, which are transported primarily by electroosmosis.

Animals↗
PubMed2001

Assessment of electrokinetic removal of heavy metals from soils by sequential extraction analysis.

Electrokinetic remediation of metal-contaminated soils is strongly affected by soil-type and chemical species of contaminants. This paper investigates the speciation and extent of migration of heavy metals in soils during electrokinetic remediation. Laboratory electrokinetic experiments were conducted using two diverse soils, kaolin and glacial till, contaminated with chromium as either Cr(III) or Cr(VI). Initial total chromium concentrations were maintained at 1000mg/kg. In addition, Ni(II) and Cd(II) were used in concentrations of 500 and 250mg/kg, respectively. The contaminated soils were subjected to a voltage gradient of 1 VDC/cm for over 200h. The extent of migration of contaminants after the electric potential application was determined. Sequential extractions were performed on the contaminated soils before and after electrokinetic treatment to provide an understanding of the distribution of the contaminants in the soils. The initial speciation of contaminants was found to depend on the soil composition as well as the type and amounts of different contaminants present. When the initial form of chromium was Cr(III), exchangeable and soluble fractions of Cr, Ni, and Cd ranged from 10 to 65% in kaolin; however, these fractions ranged from 0 to 4% in glacial till. When the initial form of chromium was Cr(VI), the exchangeable and soluble fractions of Cr, Ni and Cd ranged from 66 to 80% in kaolin. In glacial till, however, the exchangeable and soluble fraction for Cr was 38% and Ni and Cd fractions were 2 and 10%, respectively. The remainder of the contaminants existed as the complex and precipitate fractions. During electrokinetic remediation, Cr(VI) migrated towards the anode, whereas Cr(III), Ni(II) and Cd(II) migrated towards the cathode. The speciation of contaminants after electrokinetic treatment showed that significant change in exchangeable and soluble fractions occurred. In kaolin, exchangeable and soluble Cr(III), Ni(II), and Cd(II) decreased near the anode and increased near the cathode, whereas exchangeable and soluble Cr(VI) decreased near the cathode and increased near the anode. In glacial till, exchangeable and soluble Cr(III), Ni(II), and Cd(II) were low even before electrokinetic treatment and no significant changes were observed after the electrokinetic treatment. However, significant exchangeable and soluble Cr(VI) that was present in glacial till prior to electrokinetic treatment decreased to non-detectable levels near the cathode and increased significantly near the anode. In both kaolin and glacial till, low migration rates occurred as a result of contaminants existing as immobile complexes and precipitates. The overall contaminant removal efficiency was very low (less than 20%) in all tests.

Aluminum Silicates↗
PubMed1998

Electrically evoked compound action potentials of guinea pig and cat: responses to monopolar, monophasic stimulation.

We recorded electrically evoked compound action potentials (EAPs) from guinea pigs and cats using monophasic current pulses delivered by a monopolar intracochlear electrode. By using simple stimuli, we sought results that could shed light on basic excitation properties of the auditory nerve. In these acute experiments, the recording electrode was placed directly on the auditory nerve. Responses to anodic and cathodic stimulus pulses were recorded separately to evaluate stimulus polarity effects. Several polarity-dependent properties were observed. Both EAP morphology and latency were polarity-dependent, with greater latencies for cathodic stimulation. Threshold stimulus level was also polarity-dependent, but in different directions in the two species: cats had lower cathodic thresholds while guinea pigs had lower anodic thresholds. We also observed that the slopes of the EAP amplitude-level functions depended upon stimulus polarity. In most cases where EAP saturation amplitude could be measured, that amplitude was similar for anodic and cathodic stimuli, suggesting that either stimulus polarity can recruit all fibers, or at least a comparable numbers of fibers. The common findings (e.g., EAP morphology and polarity-dependent latency) observed in these two species suggest results that can be extrapolated to responses obtained in humans, while the species-specific findings (e.g., dependence of threshold on polarity) may point to underlying anatomical differences that caution against overgeneralization across species. Some of our observations also bear upon hypotheses of how electrical stimuli may excite different sites on auditory nerve fibers.

Action Potentials↗
PubMed1987

Nonthoracotomy internal defibrillation in dogs: threshold reduction using a subcutaneous chest wall electrode with a transvenous catheter electrode.

The efficacy of truncated exponential waveform shocks using a cardioverter-defibrillator catheter with and without a 13.9 cm2 subcutaneous thoracic patch electrode was examined in 10 pentobarbital-anesthetized dogs. The cardioverter-defibrillator catheter was positioned through the external jugular vein with the distal 4 cm2 shocking electrode located in the right ventricular apex and the 8 cm2 proximal electrode located in the superior vena cava. Four electrode configurations were tested: 1) distal electrode (cathode) to proximal electrode and chest wall patch (common anodes), 2) distal electrode (cathode) to chest wall patch (anode), 3) distal electrode (cathode) to proximal electrode (anode), and 4) chest wall patch (cathode) to proximal electrode (anode). The lowest randomized energy resulting in termination of alternating current-induced ventricular fibrillation on four trials at that energy was 20.2, 21.3, 27.4 and greater than 40 J, respectively, for configurations 1 through 4. The energy requirements for configurations 1, 2 and 3 were significantly lower than for configuration 4 (p less than 0.001). Additionally, configurations incorporating the distal electrode and the patch electrode (configurations 1 and 2) were significantly better than the catheter alone (configuration 3; p less than 0.05). There was no significant difference between configurations 1 and 2. In conclusion, the addition of a subcutaneous chest wall electrode to the cardioverter-defibrillator catheter significantly lowered energy requirements for defibrillation, suggesting that a nonthoracotomy approach for the automatic implantable cardioverter-defibrillator is feasible.

Animals↗
PubMed2003

Analysis of photo-pattern sensitivity in patients with Pokemon-related symptoms.

This study was designed to analyze photo-pattern sensitivity in patients who developed acute neurologic symptoms associated with watching an animated television program, "Pokemon." The 18 patients (13 females and five males) underwent electroencephalograms and photo-pattern stimulation testing, including special stimulation test batteries (strobe-pattern test and cathode ray tube-pattern test). Photo-pattern sensitivity was confirmed in 16 patients with and without seizure episodes. The strobe-pattern test including a white flickering light test (with eyes open, closed, and open or closed), and the cathode ray tube-pattern test each induced a photo-paroxysmal response in more than 80% of patients. However, with the eyes closed only, as is common in Japan, the photo-paroxysmal response induction rate with a white flickering light stimulus was significantly lower (43%). In the cathode ray tube-pattern test, higher spatial frequencies produced higher rates of photo-paroxysmal response induction. It was demonstrated that underlying photo-pattern sensitivity is more accurately investigated by our method than by standard intermittent photic stimulation alone. By characterizing underlying photo-pattern sensitivity and identifying predisposing factors more precisely, we can develop better guidelines for prevention of a second "Pokemon" incident. According to the results of the present cathode ray tube-pattern test, pattern sensitivity (especially spatial resolution) appears to also be involved in Pokemon-related symptoms, in addition to chromatic sensitivity.

Adolescent↗
PubMed1991

Effect of calcium ions on cell surface electrostatics of Bacteroides gingivalis and other oral bacteria.

Surface electrostatics of Bacteroides gingivalis and other oral bacteria were examined. A polarization circuit was employed using platinum electrodes exposed in each bacterial suspension and the number of bacteria adsorbed to the anode and cathode were then estimated. In all bacteria (B. gingivalis, Streptococcus sobrinus, S. mutans, S. salivarius, S. sanguis and Actinomyces viscosus), the number of cells adsorbed to the anode were much greater than the number of cells adsorbed to the cathode. Treating these bacteria with calcium ions tended to decrease the ratio of the number of cells adsorbed to the anode to the number of cells adsorbed to the cathode in all bacteria examined. Moreover, in the case of B. gingivalis, the number of cells adsorbed to the anode and cathode was in an inverse relationship to the number counted before calcium ion treatment. These findings indicate that the cell surfaces of oral bacteria are generally negatively charged but only the cell surface electrostatics of B. gingivalis was dramatically affected by calcium ion treatment. Thus, divalent metal bridges such as calcium bridges contribute to the adherence of the periodontopathic bacterium, B. gingivalis rather than to that of other oral bacteria including cariogenic bacteria.

Actinomyces↗
PubMed1999

Detection of caries with conventional digital imaging and tuned aperture computed tomography using CRT monitor and laptop displays.

OBJECTIVE: The purpose of this study was to compare the diagnostic performance of conventional digital images and tuned aperture computed tomography (TACT) slices in caries detection through use of cathode-ray tube monitor and laptop displays. STUDY DESIGN: Forty-two extracted posterior teeth were mounted and imaged with a direct digital radiography system. Conventional digital bitewing projections and TACT slices were acquired. Images were viewed on a high-resolution cathode-ray tube monitor and on an active-matrix laptop display. Eight observers assessed caries status of occlusal and proximal surfaces of the teeth using all combinations of image and display modality. Observers' assessments were compared with the results of histologic examination of tooth sections. Possible differences in receiver operating characteristic curve areas among displays, image modalities, observers, and surfaces were analyzed by means of analysis of variance. RESULTS: There was no statistically significant difference between the diagnostic performances provided by the cathode-ray tube monitor and laptop displays in caries detection (P = .588). In addition, the performances of digital images and TACT slices were not significantly different (P = .843). CONCLUSIONS: Modern active-matrix laptop displays provide diagnostic quality for caries detection comparable to that obtainable with cathode-ray tube monitors.

Analysis of Variance↗
PubMed2003

Double peak sensory responses at submaximal stimulation.

OBJECTIVE: The objective of the study was to obtain knowledge about the different physiological situations where a double peak sensory response normally occurs and to better understand the significance of this particular sensory response. METHODS: In 14 healthy subjects, conventional orthodromic sensory nerve conduction studies were performed on the median and ulnar nerves using submaximal stimulation. Various stimulus strengths, polarity, electrode positions and local anaesthesia were used to clarify the generation of the two peaks. RESULTS: When the cathode and the anode were independently moved in distal direction, the first and the second peaks moved distally, respectively. This occurred for conventional and reversed position of the electrode. Anodal stimulation was ineffective after local skin anaesthesia. CONCLUSIONS: Our experiments seem to indicate that the double response represents the two stimulation sites, under the cathode and the anode, respectively. Obviously the double response can only occur if different axons are stimulated under the two poles. The cathode and the anode do not seem preferably to stimulate fast or slow axons. Studies with superficial anaesthesia may indicate that the cathode stimulates the sensory nerve directly while the anode mainly stimulates superficial structures, skin sensory receptors or intradermal nerve terminals.

Adult↗
PubMed2001

Analysis of dark spots growing in organic EL devices by time-of-flight secondary ion mass spectrometry.

Chemical structural analysis of tape-stripped surfaces at dark spots growing in organic electroluminescent (EL) devices during exposure to the atmosphere was done by time-of-flight secondary ion mass spectrometry (OF-SIMS). The EL devices consist of indium-tin-oxide, triphenylamine-tetramer, tris(8-hydroxyquinoline)aluminum (Alq3), and a Mg-Ag cathode deposited in order under vacuum on a glass substrate. It was found that the interface between the Alq3 layer and the Mg-Ag cathode was exposed as a result of tape-stripping, where a large number of dark spots were observed on both sides. Secondary ion images of O-, Mg+, and Alq2+ were observed from the dark spots on the cathode side. On the other hand, Mg+ and O- images with a nucleus in the center were observed from the Alq3 side. It is concluded from the results that the constituent element Mg of the cathode was oxidized at the interface adjacent to the Alq3 layer during exposure to the atmosphere, forming a dark spot with a nucleus in the center. Finally, it was confirmed that the TOF-SIMS analysis of the tape-stripped surface is useful for the analysis of the mechanism of dark spot formation.

Journal Article↗
PubMedDate not supplied

A comparison of air and hydrogen peroxide oxygenated microbial fuel cell reactors.

In this study, a two-compartment continuous flow microbial fuel cell (MFC) reactor was used to compare the efficiencies of cathode oxygenation by air and by hydrogen peroxide. The MFC reactor had neither a proton-selective membrane nor an electron transfer mediator. At startup, the cathodic compartment was continuously aerated and the anodic compartment was fed with a glucose solution. An increase of electrical power generation from 0.008 to 7.2 mW m(-2) of anode surface with a steady-state potential of 215-225 mV was observed within a period of 12 days. The performance of the air-oxygenated MFC reactor progressively declined over time because of biofilm proliferation in the cathodic compartment. Oxygenation of the cathodic compartment using 300 mL d(-1) of 0.3% hydrogen peroxide solution resulted in a power density of up to 22 mW m(-2) (68.2 mA m(-2)) of anode surface at a potential of 340-350 mV. The use of H2O2 for oxygenation was found to improve the long-term stability of the MFC reactor.

Air↗
PubMed2003

Electrolyte management for effective long-term electro-osmotic transport in low-permeability soils.

Electro-osmosis, a coupled-flow phenomenon in which an applied electrical potential gradient drives water flow, may be used to induce water flow through fine-grained sediments. Test cell measurements of electro-osmotic transport in clayey cores extracted from the 27-31 m depth range of the Lawrence Livermore National Laboratory site indicate the importance of pH control within the anode and cathode reservoirs. In our first experiment, pH was not controlled. As a result, carbonate precipitation and metals precipitation occurred near the cathode end of the core, with acidification near the anode. The combination of these acid and base reactions led to the decline of electro-osmotic flow by a factor of 2 in less than one pore volume. In a second experiment, long-term water transport (>21 pore volumes) at stable electro-osmotic conductivity (k(eo) approximately 1 x 10(-9) m2/s-V) was effected with anode reservoir pH > 8, and cathode reservoir pH < 6. Hydraulic conductivity (k(h)) of the same core was 4 x 10(-10) m/s under a 0.07 MPa hydraulic gradient without electro-osmosis. Stable electro-osmotic flow was measured at a velocity of 4 x 10(-7) m/s under a 4 V/cm voltage gradient, and no hydraulic gradient-3 orders of magnitude greater than the hydraulic flow. We also observed chloroform production in the anode reservoir, resulting from electrochemical production of chlorine gas reacting with trace organics. The chloroform was transported electro-osmotically to the cathode, without measurable loss to adsorption, volatilization, or degradation.

Chloroform↗
PubMed2003

A biofuel cell with electrochemically switchable and tunable power output.

An electroswitchable and tunable biofuel cell based on the biocatalyzed oxidation of glucose is described. The anode consists of a Cu(2+)-poly(acrylic acid) film on which the redox-relay pyrroloquinoline quinone (PQQ) and the flavin adenine dinucleotide (FAD) cofactor are covalently linked. Apo-glucose oxidase is reconstituted on the FAD sites to yield the glucose oxidase (GOx)-functionalized electrode. The cathode consists of a Cu(2+)-poly(acrylic acid) film that provides the functional interface for the covalent linkage of cytochrome c (Cyt c) that is further linked to cytochrome oxidase (COx). Electrochemical reduction of the Cu(2+)-poly(acrylic acid) films (applied potential -0.5 V vs SCE) associated with the anode and cathode yields the conductive Cu(0)-poly(acrylic acid) matrixes that electrically contact the GOx-electrode and the COx/Cyt c-electrode, respectively. The short-circuit current and open-circuit voltage of the biofuel cell correspond to 105 microA (current density ca. 550 microA cm(-2)) and 120 mV, respectively, and the maximum extracted power from the cell is 4.3 microW at an external loading resistance of 1 kOmega. The electrochemical oxidation of the polymer films associated with the electrodes (applied potential 0.5 V) yields the nonconductive Cu(2+)-poly(acrylic acid) films that completely block the biofuel cell operation. By the cyclic electrochemical reduction and oxidation of the polymer films associated with the anode and cathode between the Cu(0)-poly(acrylic acid) and Cu(2+)-poly(acrylic acid) states, the biofuel cell performance is reversibly switched between "ON" and "OFF" states, respectively. The electrochemical reduction of the Cu(2+)-polymer film to the Cu(0)-polymer film is a slow process (ca. 1000 s) because the formation and aggregation of the Cu(0)-clusters requires the migration of Cu(2+) ions in the polymer film and their reduction at conductive sites. The slow reduction of the Cu(2+)-polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell. The electron-transfer resistances of the cathodic and anodic processes were characterized by impedance spectroscopy. Also, the overall resistances of the biofuel cell generated by the time-dependent electrochemical reduction process were followed by impedance spectroscopy and correlated with the internal resistances of the cell upon its operation.

Bioelectric Energy Sources↗
PubMed2004

A four-electron O(2)-electroreduction biocatalyst superior to platinum and a biofuel cell operating at 0.88 V.

O2 was electroreduced to water, at a true-surface-area-based current density of 0.5 mA cm-2, at 37 degrees C and at pH 5 on a "wired" laccase bioelectrocatalyst-coated carbon fiber cathode. The polarization (potential vs the reversible potential of the O2 /H2O half-cell in the same electrolyte) of the cathode was only -0.07 V, approximately one-fifth of the -0.37 V polarization of a smooth platinum fiber cathode, operating in its optimal electrolyte, 0.5 M H2SO4. The bioelectrocatalyst was formed by "wiring" laccase to carbon through an electron conducting redox hydrogel, its redox functions tethered through long and flexible spacers to its cross-linked and hydrated polymer. Incorporation of the tethers increased the apparent electron diffusion coefficient 100-fold to (7.6 +/- 0.3) x 10-7 cm 2 s-1. A miniature single-compartment glucose-O2 biofuel cell made with the novel cathode operated optimally at 0.88 V, the highest operating voltage for a compartmentless miniature fuel cell.

Journal Article↗
PubMed2002

Deoxyhemoglobin-mediated lipid oxidation in washed fish muscle.

Deoxyhemoglobin-mediated lipid oxidation was studied by comparing the pro-oxidative activity of anodic and cathodic hemoglobins from trout in a washed cod muscle model system. At pH 6.3, cathodic hemoglobins were nearly fully oxygenated while anodic hemoglobins were poorly oxygenated. Anodic hemoglobins initiated lipid oxidation in washed cod muscle much more rapidly than cathodic hemoglobins, as measured by thiobarbituric acid reactive substances (TBARS) formation. Moreover, anodic hemoglobins appeared to oxidize more rapidly as compared to cathodic hemoglobins in the washed cod muscle model system, as measured by a decrease in redness (a value). A more pronounced pro-oxidative activity of deoxyhemoglobin as compared to oxyhemoglobin was confirmed by accelerated lipid hydroperoxide and TBARS formation in the washed cod muscle model system upon combined addition of anodic hemoglobins and adenosine triphosphate, which is known to lower the oxygenation of anodic hemoglobins at pH 7.2, as compared to only addition of anodic hemoglobins to the washed cod muscle. These studies suggest that deoxyhemoglobin is more pro-oxidative than its oxygenated counterpart at pH values found in postmortem fish muscle.

Animals↗
PubMed2005

A photoelectronic switching device using a mixed self-assembled monolayer.

A cathodic-anodic biway photoelectronic device has been successfully constructed using a self-assembled monolayer (SAM). The SAM consists of two kinds of photofunctional thiol derivatives, a ruthenium complex-viologen linked compound (RuVS) and a phthalocyanine derivative (PcS), on a gold electrode. Structural characterization of the SAM has been carried out by absorption spectroscopy, cyclic voltammetry, and differential pulse voltammetry. Photocurrent responses were measured in the presence of methyl viologen (MV2+) and oxygen as electron acceptors and triethanolamine (TEOA) as a sacrificial reagent. For the SAM of RuVS alone, intramolecular electron transfer (ET) was superior to intermolecular ET, resulting in anodic photocurrents even in the presence of MV2+ and oxygen at 0 V vs Ag/AgCl. On the contrary, only cathodic photocurrents were observed at 0 V for the SAM of PcS alone. Photocurrents from the mixed SAM of RuVS and PcS were roughly the sum of individual photocurrents from RuVS and PcS. In fact, photocurrents from the mixed SAM of RuVS and PcS were observed in the anodic direction below approximately 550 nm, and in the cathodic direction above approximately 550 nm at 0 V vs Ag/AgCl. In the case of the mixed SAM of RuS (ruthenium complex disulfide) and PcS, only cathodic photocurrents were observed at 0 V vs Ag/AgCl, due to the lack of an intramolecular ET pathway. The results indicate that in the mixed SAM of RuVS and PcS both dyes can individually function for opposite photocurrent generation. We have also applied the mixed SAM as a photoelectronic logic device by using two LEDs (470 and 640 nm). The system clearly operated as an XOR logic device.

Journal Article↗
PubMed1995

Iontophoresis enhances the transport of acyclovir through nude mouse skin by electrorepulsion and electroosmosis.

PURPOSE: Iontophoresis was employed for enhancing the transdermal delivery of acyclovir through nude mouse skin in vitro, with the aim of understanding the mechanisms responsible for drug transport, in order to properly set the conditions of therapeutical application. METHODS: Experiments were done in horizontal diffusion cells, using as donor a saturated solution of acyclovir at two different pH values (3.0 and 7.4). Different electrical conditions (current density and polarity) were employed. RESULTS: At pH 3.0, acyclovir anodal transport was due to electrorepulsion, since acyclovir was 20% in the protonated form. In acyclovir anodal iontophoresis at pH 7.4 the main mechanism involved was electroosmosis, since the drug was substantially unionized and the negative charge of the skin at this pH caused the electroosmotic flow to be from anode to cathode. In the case of cathodal iontophoresis at pH 3.0, acyclovir transport was enhanced approx. seven times, due to the presence of an electroosmotic contribution caused by the reversal of the charge of the skin. At pH 7.4 during cathodal iontophoresis acyclovir transport was not enhanced because the electroosmotic flow was in the opposite direction, compared to drug electric transport, i.e. anode to cathode. The increased skin permeability caused by current application was demonstrated to be less important than electrorepulsion and electroosmosis. CONCLUSIONS: Anodal iontophoresis shows potential applicability for enhancing acyclovir transport to the skin, considering that both electric transport and electroosmosis can be used by appropriately setting the pH of the donor.

Acyclovir↗
PubMed1993

Electrocutaneous spatial integration at suprathreshold levels: an additive neural model.

The effect of cathode size on estimates of the magnitude of electrocutaneous stimulation were studied. The 24 Ss made magnitude estimates for combinations of 6 cathode sizes (2.5-30 mm diameter) and 5 currents (1.5-3.3 times the threshold). Estimates for small cathodes were consistently smaller but grew more rapidly than those for intermediate and large cathodes. From the results, contours were constructed showing how area and current trade off to maintain apparent intensity. These area-current contours suggest that supersummation prevails at low estimation levels and complete summation tasks place at high levels. An additive neural model is proposed to account for the results and is also applied to other somatosensory systems.

Adolescent↗