Pupillary dilation as a measure of attention: a quantitative system analysis

It has long been known that the pupil dilates as a consequence of attentional effort. But the function that relates attentional input to pupillary output has never been the subject of quantitative analysis. We present a system analysis of the pupillary response to attentional input. Attentional input is modeled as a string ofattentional pulses. We show that the system is linear; the effects of input pulses on the pupillary response are additive. The impulse response has essentially a gamma distribution with two free parameters. These parameters are estimated; they are fairly constant over tasks and subjects. The paper presents a method of estimating the string of attentional input pulses, given some average pupillary output. The method involves the technique of deconvolution; it can be implemented with a public-domain software package, Pupil.     

Perisaccadic parietal and occipital gamma power in light and in complete darkness

Our objective was to determine perisaccadic gamma range oscillations in the EEG during voluntary saccades in humans. We evaluated occipital perisaccadic gamma activity both in the presence and absence of visual input, when the observer was blindfolded. We quantified gamma power in the time periods before, during, and after horizontal saccades. The corresponding EEG was evaluated for individual saccades and the wavelet transformed EEG averaged for each time window, without averaging the EEG first. We found that, in both dark and light, parietal and occipital gamma power increased during the saccade and peaked prior to reaching new fixation. We show that this is not the result of muscle activity and not the result of visual input during saccades. Saccade direction affects the laterality of gamma power over posterior electrodes. Gamma power recorded over the posterior scalp increases during a saccade. The phasic modulation of gamma by saccades in darkness--when occipital activity is decoupled from visual input--provides electrophysiological evidence that voluntary saccades affect ongoing EEG. We suggest that saccade-phasic gamma modulation may contribute to short-term plasticity required to realign the visual space to the intended fixation point of a saccade and provides a mechanism for neuronal assembly formation prior to achieving the intended saccadic goal. The wavelet-transformed perisaccadic EEG could provide an electrophysiological tool applicable in humans for the purpose of fine analysis and potential separation of stages of 'planning' and 'action'.     

From darkness to light: children speak of divine encounter

Abstract

Studies have shown that children share both positive and dark spiritual experiences. The former dominates the literature but whilst the need to address the dark side of spirituality has been raised it has not, as yet, been dealt with as widely as the more positive aspects. This paper draws on an empirical study with 44 children aged 8–11 who were interviewed in school after visiting a sacred space. Three key themes arising from their conversations are covered in this paper: divine encounter; physical feelings and fear. It is argued that the most appropriate way of understanding these phenomena is to draw on different fields and disciplines, notably although not exclusively, theology, psychoanalysis, psychology and neuroscience. The paper concludes that it is important to recognise both the light and dark and the blurred boundaries between them, in addition to different ways of perceiving them, in order to understand the whole child.     

Human and institutional transformations: Catholic hospitals becoming 'a light in the the darkness.

Catholic health care institutions in the United States and Canada face internal and external challenges to their continued existence. Confronted by these external and internal challenges, Catholic hospitals in the United States and Canada have been pressed to identify what is distinctive about the Catholic contribution to health care and to consider whether existing institutional structures and partnerships foster what is distinctive. The author looks at the essays in this volume by Dennis Brodeur, Clarke E. Cochran, and Christopher J. Kauffman, and suggests that there is little agreement, even among Catholics, on such fundamental issues. The aim of this article is to highlight three important and often overlooked ideas raised by the authors, to relate them to the Canadian context by means of a story, and to pose questions for further discussion.     

Transcendental pride and Luciferism: On being bearers of light and powers of darkness

Continental Philosophy Review - The ancient theme of the metaphysical-theological extremes of being-human is revisited by asking about the condition for the readiness to engage in the form of...     

Golden hamsters on the eight-arm maze in light and darkness: The role of dead reckoning

This paper examines whether golden hamsters can rely on dead reckoning (getting positional information from updated signals generated during locomotion) on an eight-arm maze. Two groups of hamsters were tested: Group L under ordinary room light, Group D in darkness. To enhance the role of dead reckoning, each subject could climb from its own home cage onto the central platform of the maze. In a first experimental phase (15 trials), the L subjects learned to master the maze through developing a locomotor rule (arm chaining) after three to four trials. The D subjects developed arm chaining less readily and fluctuated more in their performance than did the L subjects. In a second experimental phase (15 trials), four arms were blocked at the beginning of each trial. In both experimental groups the performance decreased, yet remained well above chance level. Success and arm chaining were positively correlated in Phase 1 and negatively correlated with success in Phase 2. We assume that in Phase 2 the L subjects switched to the predominant use of visual cues, and the D subjects to dead reckoning.     

Pupillary changes during recall in children

Seven children aged 7–9 years were auditorily presented five-digit numbers for retention intervals of 0 and 10 sec. Pupil size was recorded during stimulus presentation, retention interval, and recall of items. Findings indicate that pupil dilation occurs during encoding and retrieval of stimulus items with pupillary constriction occurring during retention of the items. The pupillary change functions obtained with children were found to be very similar to those obtained with older subjects.     

Pupillary responses in a pitch-discrimination task

Pupils were measured while observers made pitch judgments under the method of constant stimuli. A substantial dilation occurs immediately after the presentation of the comparison tone, and the size of this response is closely correlated to the difficulty of the discrimination. Baseline changes occur within each block of trials, but have little effect on the magnitude of dilations. Responses to redundant stimuli, including the standard itself, decrease during the experimental session. The results support the validity of pupillary measurements as an index of processing load.     

Pupillary measurement and release from proactive inhibition.

One of the explanations of release from proactive inhibition in short-term memory is that the subjects re-attend to the items on the release trial because the items are different from the previous ones. It is further assumed that this increase in attention causes the relase items to be learned better than the preceding items. This experiment measured the pupils of the subjects' eyes while they were participating in a proactive-inhibition release-type task. The results showed no increase in attention, as indexed by pupil size, on the release trial. This did not support the attentional explanation of the proactive-inhibition release phenomenon.     

Pupillary and heart rate reactivity in children with minimal brain dysfunction

This study attempted to replicate and extend previous findings on autonomic arousal and responsivity in children with diagnoses of minimal brain dysfunction (MBD). Pupil size, heart rate, skin conductance, and skin temperature were recorded from 32 MBD and 45 control children during a session that included presentation of visual stimuli, simple reaction time (RT), a cold pressor procedure, and rest periods. The MBD children were tested both off and on clinical dosages of stimulant drugs in a crossover design. Evidence of higher than normal arousal levels in the unmedicated MBD Ss was obtained from resting skin conductance and, more tenuously, from pupil size. Lower phasic responsivity in the MBD children was evidenced by slower RT, less cardiac deceleration to both light and RT stimuli, and smaller pupil dilation to the RT stimuli. Spontaneous pupillary constrictions during rest periods, presumably indicating drowsiness, were observed about equally in MBD and control children. Stimulant drugs raised arousal levels but did not reverse the responsivity deficits. The lower phasic reactivity in the MBD group and the effects of stimulant drugs on arousal indices confirm earlier reports. The finding of higher arousal in drug-free MBD children is incompatible with the low arousal hypothesis of MBD but is consistent with a previous report of the effects of a stimulating environment on these children.This work was supported in part by a grant from the Ittleson Family Foundation. The authors thank Frank Abate for technical assistance.     

Oculomotor adjustments in darkness and the specific distance tendency

Two experiments were performed to investigate the relationship between the oculomotor adjustments assumed in total darkness and perceived distance under reduced visual conditions. Experiment I compared the dark focus of accommodation with the perceived distance of a monocular light point presented in a dark environment. Experiment II compared the convergence angle assumed in darkness (dark convergence) with the perceived distance of the light point. Both accommodation and convergence were found to assume intermediate values in darkness. Perceived distance of the monocular light point was significantly correlated with dark convergence and unrelated to the dark focus of accommodation. It was suggested that ocular vergence is a major determinant of perceived distance under reduced visual conditions, and thus provides a possible mechanism for the specific distance tendency.     

Eye position affects audio-visual fusion in darkness

We investigated the frame of reference involved in audio-visual (AV) fusion over space. This multisensory phenomenon refers to the perception of unity resulting from visual and auditory stimuli despite their potential spatial disparity. The extent of this illusion depends on the eccentricity in azimuth of the bimodal stimulus (Godfroy et al, 2003 Perception 32 1233-1245). In a previous study, conducted in a luminous environment, Roumes et al 2004 (Perception 33 Supplement, 142) have shown that variation of AV fusion is gaze-dependent. Here we examine the contribution of ego- or allocentric visual cues by conducting the experiment in total darkness. Auditory and visual stimuli were displayed in synchrony with various spatial disparities. Subjects had to judge their unity ('fusion' or 'no fusion'). Results showed that AV fusion in darkness remains gaze-dependent despite the lack of any allocentric cues and confirmed the hypothesis that the reference frame of the bimodal space is neither head-centred nor eye-centred.