Robert Galambos

Human auditory evoked potentials. I: Evaluation of components

Abstract Fifteen distinct components can be identified in the scalp recorded average evoked potential to an abrupt auditory stimulus. The early components (I–VI) occuring in the first 8 msec after a stimulus represent the activation of the cochlea and the auditory nuclei of the brainstem. The middle latency components (N o , P o , N a , P a , N b ) occuring between 8 and 50 msec after the stimulus probably represent activation of both auditory thalamus and cortex but can be seriously contaminated by concurrent scalp muscle reflex potentials. The longer latency components (P 1 , N 1 , P 2 , N 2 ) occuring between 50 and 300 msec after the stimulus are maximally recorded over fronto-central scalp regions and seem to represent widespread activation of frontal cortex.

Tandem-Scanning Reflected-Light Microscope*

Reflected-light microscopy of semitransparent material, such as unstained nervous tissue, is usually unsatisfactory because of low contrast and light scattering. In a new microscope both the object plane and the image plane were scanned in tandem so that only light reflected from the object plane was included in the image. The object was illuminated with nearly incoherent light passing through holes in one side of a rotating scanning disk (Nipkow wheel) which was imaged by the objective into the object plane. Reflected-light images of these spots were conducted to the opposite side of the same disk. Light could pass from the source to the object plane, and from the object to the image plane, only through optically congruent holes on opposite side of the rotating disk. The image obtained had better contrast and sharpness for some semitransparent material than possible in usual reflected-light microscopy.

Eye movement artifact in the CNV

Abstract During the preparatory interval between a warning click and a tone burst that signalled a lever press, a slow negative potential shift (CNV) was recorded from the scalp in ten normal adults. When the eyes were closed, involuntary eye movements during the click-tone interval consistently generated potential shifts which spread from the corneo-retinal dipole to the scalp electrodes and thereby contaminated the CNV. The CNV was quantitatively partitioned into an artifactual component caused by ocular rotation (the EAP), which summated with the second component, presumably of cerebral origin, called the “true” or tCNV. The EAP amplitudes were estimated from concurrent recordings of the electro-oculogram. In the average subject, 23% or −6.1 μV of the total CNV was comprised of EAP, and the EAP often reached from −10 to −15 μV. The accuracy of the partition was verified by comparing tCNVs recorded with eyes closed and with eyes immobilized by fixation. The CNV produced during voluntary eye movements was similarly divided into a tCNV, which was tripled in amplitude when ocular responses were made with increased speed and effort, and an EAP, which was determined solely by the amount of ocular displacement.

Event-related brain potential correlates of the processing of novel visual and auditory information in autism

Event-related brain potentials (ERPs) elicited by visual and auditory stimuli were recorded from nonretarded individuals with autism (ages 13–25 years) and age-matched normal controls. In “no-task” conditions, subjects simply looked at or listened to these stimuli; only one difference was found between subject groups. Several ERP differences between groups were found in “task” conditions; subjects pressed a button at the occurrence of target stimuli intermixed with unexpected, novel stimuli and also with expected, nonnovel stimuli. Visual ERP abnormalities in the autistic group differed from auditory abnormalities. Results suggest that (1) nonretarded autistic individuals may have a limited capacity to process novel information — they are neither hypersensitive to novel information nor misperceive it as non-novel and insignificant; (2) classification of simple visual information may be less impaired than auditory; and (3) with one exception, visual and auditory ERP abnormalities do not seem to reflect maturational delay.

Action of the Middle Ear Muscles in Normal Cats

Wires have been permanently implanted on the round window of the cochlea in cats. The voltage output of ears responding to sound stimulation has thus been made continuously available in unanesthetized animals for periods up to 4 months. By cutting the middle ear muscles of one ear and comparing its responses with those derived from the normal ear on the opposite side, it has been shown that the muscles: (1) do not appreciably influence absolute sensitivity, (2) contract to intense stimuli within 15 msec of their delivery to either ear, (3) attenuate transmission of tones between at least 500 and 3000 cps, and (4) significantly protect the ear against damage from intense sounds. Spontaneous contractions sporadically and intermittently introduce a transmission attenuation of several decibels in the resting normal cat. The stapedius muscle is much more important than the tensor tympani in producing these effects.

Habituation and Attention in the Auditory System

This chapter1 surveys some current experimental evidence regarding the neurophysiological basis of habituation and attention in the auditory system. The principal focus is upon electrophysiological studies in man although a number of relevant animal studies will also be reviewed.

Effects of stimulus and response contingencies on a surface negative slow potential shift in man

Abstract A slow wave potential (CNV) was recorded extracranially from eleven subjects during the interval between a warning stimulus (flash of light) and a burst of clicks which they terminated by pressing a lever. When subjects were not required to respond to the clicks, no CNV appeared. When they were told to turn off the clicks the CNV increased in amplitude at a rate that depended on individual prior experience with the paired flash-clicks contingency. Omission of clicks with no warning to the subjects resulted in gradual diminution of the CNV; subsequent reinstatement of clicks caused the CNV to increase in amplitude again. A significant negative correlation between size of CNV and reaction time was found over a large group of trials. The relation of the CNV to subjective expectancy and intention to respond was discussed.

Auditory perception of radio‐frequency electromagnetic fields

Absorption of pulsed microwave energy can produce an auditory sensation in human beings with normal hearing. The phenomenon manifests itself as a clicking, buzzing, or hissing sound depending on the modulatory characteristics of the microwaves. While the energy absorbed (∠10 μJ/g) and the resulting increment of temperature (∠10−6 °C) per pulse at the threshold of perception are small, most investigators of the phenomenon believe that it is caused by thermoelastic expansion. That is, one hears sound because a miniscule wave of pressure is set up within the head and is detected at the cochlea when the absorbed microwave pulse is converted to thermal energy. In this paper, we review literature that describes psychological, behavioral, and physiological observations as well as physical measurements pertinent to the microwave‐hearing phenomenon.

Optic tract lesions sparing pattern vision in cats

Abstract The visual capacities of eight cats following stereotaxic lesions that destroyed more than 85 per cent of their optic tracts were studied. Within a week post-operatively all of them resembled normal cats in most gross tests of visual abilities. Three animals tested on a flux discrimination task performed without difficulty a few days postoperatively. Two of these three also displayed skilled pattern discrimination performance despite bilateral optic lesions estimated to be 98 and 98.5 per cent complete. Postoperatively all cats presented widely dilated pupils which constricted poorly if at all to light; partial recovery of this response occurred with time.

Brainstem auditory evoked responses in man. I. Effect of stimulus rise–fall time and duration

Short latency (under 10 msec) evoked responses elicited by bursts of white noise were recorded from the scalp of human subjects. Response alterations produced by changes in the noise‐burst duration (on time), interburst interval (off time), and onset and offset shapes are reported and evaluated. The latency of the most prominent response component, wave V, was markedly delayed with increases in stimulus rise time but was unaffected by changes in fall time. Increase in stimulus duration and therefore loudness resulted in a systematic increse in latency, probably due to response recovery processes, as this effect was eliminated with increases in stimulus off time. The amplitude of wave V was insensitive to changes in signal rise and fall times, while increasing signal on time produced smaller amplitude responses only for sufficiently short off times. It is concluded that wave V of the human auditory brainstem‐evoked response is solely an onset response.Subject Classification :[43]65.59.[43].65.75.