Biomedical subjects

Sheila Gillard Crewther

Publications and source records attributed to Sheila Gillard Crewther.

6 recordsLinked to original sources

PubMed2004

Poor recall of eye-movement signals from Stage 2 compared to REM sleep: implications for models of dreaming.

An ongoing assumption made by sleep researchers is that since dreams are more often recalled on awakening from rapid eye movement (REM) sleep, dreams must occur more often during this stage of sleep. An alternative hypothesis is that cognition occurs throughout sleep, but the recall of this mentation differs on awakening. When a dream is not reported on awakening, there is no method of establishing whether it did not happen or was forgotten. The aim of the present study was to investigate this issue using an eye movement (EM) signal verification technique. Participants were instructed to produce an EM signal whenever they heard a tone. Tones were presented at increasing volume during Stage 2 and REM sleep until EM signal verification was observed. Ninety seconds after signal verification, participants were awakened and asked if they remembered hearing the tone or responding with the EM signal. Such recollection of signal verified tone (SVT) presentations was significantly less after Stage 2 sleep (65%) compared to REM sleep (100%) presentations. Furthermore, SVT recall was significantly correlated with reported dream recall frequency, suggesting the same processes involved in recalling SVTs might also underlie dream recall.

Acoustic Stimulation↗

PubMed2004

Spontaneous eyelid movements (ELMS) during sleep are related to dream recall on awakening.

The present study aimed to test whether spontaneous eyelid movements (ELMs) during stage 2 and rapid eye movement (REM) sleep are related to more frequent and vivid reports of visual mentation on awakening. Participants were awakened 15 s after an ELM was observed during ongoing REM and stage 2 sleep and immediately asked for a mentation report and to rate the visual vividness of any imagery they could remember. These reports were compared with control reports collected after a period of ELM quiescence before awakening (noELM). Significantly greater frequencies of imagery reports were collected after ELM awakenings compared with noELM awakenings from stage 2, but not REM sleep. When imagery was reported, imagery ratings were not significantly different between ELM and noELM conditions, regardless of sleep stage. The average amount of electroencephalogram (EEG) arousal 15 s after stage 2 awakenings was significantly higher in the ELM compared with noELM conditions. In addition, within the stage 2 ELM condition, EEG arousal was significantly higher when visual imagery was reported compared with reports without imagery; suggesting that the observed increase in imagery reporting from the stage 2 ELM condition could have been mediated by the level of brain arousal. Such arousal possibly provides better conditions to attend and recall previous mental activity from NREM sleep. However, there was no ELM/arousal effect within REM sleep, possibly because this state is already at maximum sleeping levels of arousal, attention and resulting dream recall.

Dreams↗

PubMed2002

Spontaneous eyelid movements during human sleep: a possible ponto-geniculo-occipital analogue?

The aim of the present study was to investigate whether eye lid movements (ELMs) were temporally related to the activity of other skeletal musculature and to proposed analogues of ponto-geniculo-occipital (PGO) waves during human sleep. Electroencephalogram (EEG), laryngeal-masseter electromyogram (EMG), electrooculgram (EOG), peri-orbital integrated potentials (PIPs), middle ear muscle activity (MEMA), ankle flexion (AF) and respiration (RESP) were monitored with ELMs during one night's sleep. Results showed that ELMs always occurred during full arousal and movement time. The ELMs that occurred during sleep were most prominent during rapid eye movement (REM) sleep, occurred at higher frequency just before REM, and were observed synchronously with other PGO analogues, supporting the notion that ELMs may be an indicator of PGO activity in humans. Of the ELMs observed during sleep, 16% showed changes in EOG, PIP, MEMA, AF and RESP simultaneously, suggesting generalized muscle activation. This coactivation of muscle activity suggested that the relationship between the muscular measures and PGO activity might be an indirect one, possibly mediated by alerting mechanisms, previously shown to be related to PGO waves in animals. Such an interpretation is consistent with the use of ELM as a widely accepted measure of the eye-blink startle response in awake human subjects.

Adolescent↗

PubMed2002

Referral rates for a functional vision screening among a large cosmopolitan sample of Australian children.

The aim of this study was to investigate the incidence of functional vision problems in a large unselected cosmopolitan population of primary school-age children and to investigate whether constant clinical criteria for functional vision problems would be implemented by the practitioners involved in the screening. Refractive errors, near point of convergence, stereopsis, strabismus, heterophoria and accommodative facility were assessed for 2697 children (3-12 years) of varying racial backgrounds living in Australia. The spherical component of the refractive error ranged from -7.75 to +9.50 D (mean +0.54 D, +/-0.79) with a distribution skewed towards hypermetropia; astigmatism ranged from 0 to 4.25 D (mean -0.16 D, +/-0.35). There was a trend towards less hypermetropia and slightly more astigmatism with age. Mean near point of convergence was 5.4+/-2.9 cm, heterophoria at far and near was 0.12+/-1.58delta exophoria and 1.05+/-2.53delta exophoria, respectively, 0.55% of children exhibited vertical phoria at near >0.5delta, accommodative facility ranged from 0 to 24 cycles per minute (cpm) (mean 11.2 cpm, +/-3.7), stereopsis varied from 20 to 800 s (") of arc with 50% of children having 40" or better. The prevalence of strabismus was particularly low (0.3%). Twenty percent of the children were referred for further assessment based on criteria of one or more of: stereopsis >70", accommodative facility <8 cpm, near point of convergence (NPC) >9 cm, near exophoria >10delta or near esophoria >5delta, shift in eso or exophoria > or = 4delta between distance and near, astigmatism > or = 1 D, myopia more than -0.75 D, or hyperopia >+1.50 D. Post-hoc analysis of the record cards seeking the reason for further assessment indicates that referrals appear to have been based upon clinical intuition rather than on a set number of borderline or unsatisfactory results.

Accommodation, Ocular↗

PubMedDate not supplied

Strabismic amblyopia. Part 1. Psychophysics.

This is a two-part survey of current literature concerning strabismic amblyopia. The aim of this review is to bring the optometric practitioner up to date on the status of scientific research into strabismic amblyopia. Part 1 in this series discusses research into strabismic amblyopia from the viewpoint of psychophysical experiments that investigate both spatial and temporal behavioural deficits accompanying strabismic amblyopia. These include deficits in contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Part 2 will evaluate neural processing in regard to strabismic amblyopia. It will discuss current understanding of aspects of central processing of visual information and theories regarding neural sites and mechanisms involved in amblyopia.

Journal Article↗

PubMedDate not supplied

Strabismic amblyopia. Part 2. Neural processing.

This is the second of a two-part survey of current literature concerning strabismic amblyopia. The aim of this review is to bring the optometric community up to date on the status of scientific research into strabismic amblyopia. Part 1 in this series discussed research into strabismic amblyopia from the viewpoint of psychophysical experiments, which investigate both spatial and temporal behavioural deficits accompanying strabismic amblyopia. These include deficits in contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Part 2 concerns neural processing in regards to strabismic amblyopia. It discusses current understanding of more fundamental aspects of central processing of visual information and in particular current theories regarding neural sites and mechanisms involved in amblyopia.

Journal Article↗