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Biomedical subjects

J R Johnstone

Publications and source records attributed to J R Johnstone.

At least 19 recordsLinked to original sources
PubMed1987

Epidemiology of AIDS.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1979

Cochlear action potential threshold and single unit thresholds.

There is a close correlation between the sound pressure of tone burst required to affect a primary auditory neuron at its characteristic frequency and that which will produce a detectable N1 response at the same frequency. Units with thresholds from 80--0 db SPL (recorded from damaged and undamaged cochleas) were 0--20 dB , respectively, more sensitive than the action potential response.

Action Potentials↗
PubMed1978

A comparison of threshold and suprathreshold appearance of gratings with components in the low and high spatial frequency range.

1. The appearance of square gratings with some of their Fourier components missing has been investigated for both threshold and suprathreshold contrasts.2. If high frequency components are removed from a square grating there is only a very small effect on the detection threshold, or suprathreshold appearance, unless the components are visible by themselves.3. If the fundamental frequency is removed from a square-wave grating which has a spatial frequency lower than 1 cycle per degree (c/d) the contrast sensitivity is not altered. This is a generalisation of the Craik-Cornsweet illusion. If the contrast is raised above the detection threshold the grating is indistinguishable from a square grating, unless the contrast is high enough to see the fundamental when it is presented alone.4. If the fundamental is removed from a square grating which has a spatial frequency higher than 1 c/d the contrast threshold and the appearance at all contrasts are changed. At threshold it appears as a sinusoidal grating of three times the fundamental frequency. The threshold is dictated solely by the amplitude of the third harmonic. If the contrast is further raised, so that the fifth harmonic also reaches threshold, the periodictiy of the fundamental is seen.5. Therefore, gratings of many different luminance profiles (including the Craik-Cornsweet profile) all produce the perception of a square grating simply because those missing components which would be required in each case to produce a perfect square are by themselves undetectable. The visual system responds as though hardwired to detect square gratings and edges by means of quasi-Fourier analysis.6. These results are analagous to the missing fundamental, or residue, effect in hearing.

Humans↗
PubMed1970

Reinnervated eye muscles do not respond to impulses in foreign nerves.

Normal movements return to carp eyes after section and regeneration of the IIIrd and IVth nerve trunks. Two months after reinnervation, records of impulses in the inferior oblique nerve during tilting of the body show activity of the normal motoneurons to that muscle, together with discharge patterns characteristic of the antagonistic superior oblique and some of the rectus muscles. These axons must have found their way into the inferior oblique trunk during sprouting at the lesion and must be maintained after reinnervation. Impulses from foreign axons are without detectable effect on eye movement and therefore must be blocked at their termination in the muscle. Previous study of cross-innervated and doubly innervated fish eye muscles revealed only structurally normal neuromuscular junctions. Transmission from foreign junctions in multiply innervated muscle is blocked by competitive molecular recognition and control mechanisms that do not cause degeneration.

Animals↗