Biomedical subjects

Michael J Morgan

Publications and source records attributed to Michael J Morgan.

12 recordsLinked to original sources

PubMed2006

Stochastic re-calibration: contextual effects on perceived tilt.

The human visual system exaggerates the difference between the tilts of adjacent lines or grating patches. In addition to this tilt illusion, we found that oblique flanks reduced acuity for small changes of tilt in the centre of the visual field. However, no flanks--regardless of their tilts--decreased sensitivity to contrast. Thus, the foveal tilt illusion should not be attributed to orientation-selective lateral inhibition. Nor is it similar to conventional crowding, which typically does not impair letter recognition in the fovea. Our observers behaved as though the reference orientation (horizontal) had a small tilt in the direction of the flanks. We suggest that the extent of this re-calibration varies randomly over trials, and we demonstrate that this stochastic re-calibration can explain flank-induced acuity loss in the fovea.

Contrast Sensitivity↗

PubMed2006

Differential changes of magnocellular and parvocellular visual function in early- and late-onset strabismic amblyopia.

PURPOSE: Studies in nonhuman primates show that monocular visual deprivation starting at different ages has different effects on cells in the parvocellular and magnocellular laminae of the lateral geniculate nucleus. The present study used color and luminance contrast sensitivity (CS) measurements to look for differences in parvocellular- and magnocellular-related visual function in human subjects with strabismic amblyopia. METHODS: Fifteen subjects with early- and 14 with late-onset strabismic amblyopia and similar ranges of visual acuity were studied, together with 15 subjects with normal vision. Contrast sensitivities were measured to an equiluminant (L-M cone-modulated) grating with slow onset and an achromatic (L+M cone-modulated) 0.8-cpd grating with rapid onset using an adaptive METHOD RESULTS: Luminance and color CS were lower in the amblyopic eyes than in the fellow eyes of all amblyopes. For luminance CS, this was due both to an increase in sensitivity of the fellow eye and to a reduction in sensitivity in the amblyopic eye. Color CS was greatly reduced in the amblyopic and fellow eyes of subjects with strabismic amblyopia of early- and late onset compared with subjects with normal vision. The reduction in color CS compared with luminance CS was significantly greater in eyes with late- rather than early-onset amblyopia. CONCLUSIONS: Parvocellular and magnocellular function are differentially affected in the amblyopic and fellow eyes of subjects with strabismic amblyopia. The difference is more marked in late-onset amblyopia than in early-onset amblyopia.

Adolescent↗

PubMed2006

The sub-acute effects of recreational ecstasy (MDMA) use: a controlled study in humans.

All previous studies of the sub-acute effects of ecstasy have failed to adequately control for group differences in psychopathology and past and concurrent substance use. The present study was designed to avoid these limitations. At an initial pre-drug baseline, a sample of 38 regular ecstasy users provided full substance histories and completed measures of personality and self-reported psychopathology. We then collected daily subjective measures of mood, cognitive impairment, restless sleep, sexual desire, craving for ecstasy and concomitant use of other substances for the next 9 days. The 20 participants who subsequently opted to take ecstasy during the 9-day assessment period reported modest sub-acute effects of ecstasy on negative mood and subjective cognitive impairment compared to those who did not after controlling for baseline group differences in psychopathology and frequency of ecstasy use. There were no significant sub-acute effects of ecstasy on interest in sexual activity or craving for ecstasy. After further controlling for co-use of alcohol with ecstasy, and the sub-acute effects of ecstasy on sleep, the sub-acute effect on mood remained marginally statistically significant but the subacute effect on cognitive impairment did not. The present findings suggest that the sub-acute effects of ecstasy in regular recreational users are relatively modest and transient but that such genuine effects may have been masked by, perhaps more clinically significant, chronic sequelae of regular ecstasy use in all previous studies of recreational ecstasy users.

Adolescent↗

PubMed2005

Inferring the time-dependent complex Ginzburg-Landau equation from modulus data.

We present a formalism for inferring the equation of evolution of a complex wave field that is known to obey an otherwise unspecified -dimensional time-dependent complex Ginzburg-Landau equation, given field moduli over various closely spaced planes. The phase of the complex wave field is retrieved via a noninterferometric method, and all terms in the equation of evolution are determined using only the magnitude of the complex wave field. The formalism is tested using simulated data for a generalized nonlinear system with a single-component complex wave field. The method can be generalized to multicomponent complex fields.

Journal Article↗

PubMed2005

Monocular texture segmentation and proto-rivalry.

When the right eye's target is the left eye's distracter and vice versa, orientation-defined search is impossible unless, as we show here, the elements are close together. More than 1s was required to find inverse-cyclopean texture boundaries when elements were arranged on a 16 x 16 grid. Less than 250 ms was required for a 24 x 24 grid covering the same area. The conventional view is that binocular rivalry requires at least 200 ms to develop, but our results suggest a more rapid access to monocular signals. We call this rapid form of access "proto-rivalry."

Eye Movements↗

PubMed2005

The role of target salience in crowding.

We studied 'crowding' in the parafovea using orientation identification of a Gabor target as the task, and flanking Gabors on an isoeccentric circle as distractors. Orientation-discrimination thresholds were raised by nearby flanking distractors. This crowding effect was increased by the number of distractors and decreased by the spatial separation between target and distractors. Crowding was greatest when the target was in the centre of the distractor array and smallest when the target was on the edge of the array. A cue indicating the position of the target improved performance when the position was otherwise unknown and the spatial separation between target and distractors was large, but the cue had no significant effect when separation was small. Increasing the contrast of the target relative to the distractors reduced crowding, but targets of smaller contrast than that of the distractors are even harder to identify than those of the same contrast. Putting the target and distractors in different depth planes decreased crowding for some observers, but there were qualitative individual differences. A large (say, 45 degrees) difference in orientation between target and distractors caused the target to 'pop out' in a presence/absence task, despite the evidence from other studies that crowding is still found in these conditions. We conclude that salience has, at best, modest effects on crowding.

Cues↗

PubMed2004

Crowding and the tilt illusion: toward a unified account.

Crowding, the difficult identification of peripherally viewed targets amidst similar distractors, has been explained as a compulsory pooling of target and distractor features. The tilt illusion, in which the difference between two adjacent gratings' orientations is exaggerated, has also been explained by pooling (of Mexican-hat-shaped population responses). In an attempt to establish both phenomena with the same stimuli--and account for them with the same model--we asked observers to identify (as clockwise or anticlockwise of vertical) slightly tilted targets surrounded by tilted distractors. Our results are inconsistent with the feature-pooling model: the ratio of assimilation (the tendency to perceive vertical targets as tilted in the same direction as slightly tilted distractors) to repulsion (the tendency to perceive vertical targets as tilted away from more oblique distractors) was too small. Instead, a general model of modulatory lateral interaction can better fit our results.

Female↗

PubMed2003

Wave-function reconstruction of complex fields obeying nonlinear parabolic equations.

We present a generalized Gerchberg-Saxton (GS) algorithm for reconstructing a (2+1)-dimensional complex scalar wave field which obeys a known nonlinear nondissipative parabolic differential equation, given knowledge of the wave-field modulus at three or more values of an evolution parameter such as time. This algorithm is used to recover the complex wave function of a (2+1)-dimensional Bose-Einstein condensate (BEC) from simulated modulus data. The Gross-Pitaveskii equation is used to model the dynamics of the BEC, with the modulus information being provided by a temporal sequence of simulated absorption images of the condensate. The efficacy of the generalized GS algorithm is examined for a wide range of simulation conditions, including strong nonlinearities, vortex states and Poisson noise. The general form of this algorithm, which allows one to reconstruct a time-dependent wave function, will be useful for studying the phase dynamics of topological defects in coherent quantum systems.

Journal Article↗

PubMed2003

Caspase- and serine protease-dependent apoptosis by the death domain of FADD in normal epithelial cells.

The adapter protein FADD consists of two protein interaction domains: a death domain and a death effector domain. The death domain binds to activated death receptors such as Fas, whereas the death effector domain binds to procaspase 8. An FADD mutant, which consists of only the death domain (FADD-DD), inhibits death receptor-induced apoptosis. FADD-DD can also activate a mechanistically distinct, cell type-specific apoptotic pathway that kills normal but not cancerous prostate epithelial cells. Here, we show that this apoptosis occurs through activation of caspases 9, 3, 6, and 7 and a serine protease. Simultaneous inhibition of caspases and serine proteases prevents FADD-DD-induced death. Inhibition of either pathway alone does not prevent cell death but does affect the morphology of the dying cells. Normal prostate epithelial cells require both the caspase and serine protease inhibitors to efficiently prevent apoptosis in response to TRAIL. In contrast, the serine protease inhibitor does not affect TRAIL-induced death in prostate tumor cells suggesting that the FADD-DD-dependent pathway can be activated by TRAIL. This apoptosis pathway is activated in a cell type-specific manner that is defective in cancer cells, suggesting that this pathway may be targeted during cancer development.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Electrophysiological and psychophysical differences between early- and late-onset strabismic amblyopia.

PURPOSE: To compare visual evoked potentials (VEPs) and contrast sensitivity in adults with early- or late-onset strabismic amblyopia. METHODS: Twelve adults with early- and 12 with late-onset strabismic amblyopia with similar ranges of visual acuity were studied. Pattern-onset VEPs to 30-minute checks were recorded at a range of contrast levels. Contrast sensitivity (CS) was measured at 3.2 cyc/deg using a two-alternative, forced-choice staircase method. RESULTS: There was no significant difference in VEP CII latency or amplitude between amblyopic and fellow eyes across all contrast levels for the early-onset group, but in the late-onset group, CII latencies were significantly longer and amplitudes smaller in the amblyopic eye. CII responses in both amblyopic and fellow eyes of the early-onset amblyopes were of significantly shorter latency and smaller amplitude than normal. In the late-onset group the CII responses from the amblyopic eye were of significantly increased latency and reduced amplitude compared with normal, whereas latency and amplitude of fellow eye responses did not differ significantly from normal. Late-onset amblyopes showed reduced CS across the central field for the amblyopic eye, but increased CS for the fellow eye compared with normal. In the early-onset group, central CS did not differ between amblyopic and fellow eyes or from normal. CONCLUSIONS: There are significant differences in the electrophysiological and psychophysical characteristics of adults with early- and late-onset strabismic amblyopia.

Adolescent↗

PubMed1988

Stimulation-produced analgesia (SPA) from brain-stem and diencephalic sites in the rat: relationships between analgesia, aversion, seizures and catalepsy.

Electrical stimulation of dorsal and dorsolateral periaqueductal gray (PAG) and internal capsule (IC) sites in the rat elicited tail flick and formalin test stimulation-produced analgesia (SPA). SPA from PAG sites was associated with aversion. SPA from IC sites was associated with aversion, generalized seizures and catalepsy. Ventrobasal nucleus of thalamus (VB) stimulation did not elicit analgesia or aversion but did induce behavior characteristic of limbic seizures. A sub-anesthetic dose of sodium pentobarbital (20 mg/kg) suppressed IC stimulation-produced generalized seizures and catalepsy, and attenuated, but did not eliminate, tail flick test analgesia. These data suggest that SPA from IC sites in the rat is partially confounded with reduced responsivity. The hypothesis that SPA associated with aversion may represent a form of stress-induced analgesia is discussed.

Analgesia↗

PubMedDate not supplied

Economic applications of an electronic clinical database for nurse practitioner students.

PURPOSE: To describe the development of a Web-based clinical database that incorporates the standardized nursing languages (SNLs) used by nurse practitioner students, describe outcomes relative to the SNLs, and discuss economic aspects of outcome data. METHODS: A mix of retrospective and prospective data of all outcomes for several cohorts (95 students, 17,193 records) comprised the data set. FINDINGS: There is wide variation in use of SNLs as well as terminologies from other disciplines. The economic impact of patient encounters could be substantial. CONCLUSIONS: A Web-based clinical log provides an opportunity for NP students to collect and analyze data on clinical encounters. Considerable resources must be invested in order to expand the use and sophistication of eClinicaLog.

Consumer Behavior↗