The Effect of Dark Adaptation and of Light Upon the Electric Threshold of the Human Eye

Barlow, H. B.; Kohn, Henry I.; Walsh, Eric

doi:10.1152/ajplegacy.1947.148.2.376

Cited by 19 publications

(6 citation statements)

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“…Dark adaptation and threshold determination. Before stimulus exposure, subjects were seated in the MSR and dark-adapted for 30 min (35). Given that stimuli were brief (≤100 ms) and small (<1°), delivering them in the dark optimized the signal-to-noise ratio of elicited MEG activity.…”

Section: Methodsmentioning

confidence: 99%

Cortical response tracking the conscious experience of threshold duration visual stimuli indicates visual perception is all or none

Sekar

Findley

Poeppel

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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At perceptual threshold, some stimuli are available for conscious access whereas others are not. Such threshold inputs are useful tools for investigating the events that separate conscious awareness from unconscious stimulus processing. Here, viewing unmasked, threshold-duration images was combined with recording magnetoencephalography to quantify differences among perceptual states, ranging from no awareness to ambiguity to robust perception. A four-choice scale was used to assess awareness: "didn't see" (no awareness), "couldn't identify" (awareness without identification), "unsure" (awareness with low certainty identification), and "sure" (awareness with high certainty identification). Stimulus-evoked neuromagnetic signals were grouped according to behavioral response choices. Three main cortical responses were elicited. The earliest response, peaking at ∼100 ms after stimulus presentation, showed no significant correlation with stimulus perception. A late response (∼290 ms) showed moderate correlation with stimulus awareness but could not adequately differentiate conscious access from its absence. By contrast, an intermediate response peaking at ∼240 ms was observed only for trials in which stimuli were consciously detected. That this signal was similar for all conditions in which awareness was reported is consistent with the hypothesis that conscious visual access is relatively sharply demarcated.cognition | vision C onscious visual representations must be generated rapidly enough to affect behavior advantageously. Thus, vision must be fast. However, the network activation that supports visual perception is complex and involves many spatially segregated brain areas (1). As a result, certain integration delays must ensue for successful perceptual analysis to be achieved. An experimental paradigm was thus designed to address the temporal and neuronal conditions required for a rapid, high-level visual response.Several previous studies suggest that visual perception relies primarily on the early activation of occipital cortices (2-4). Others show that it results from the late activation (5, 6) of temporal (7), parietal, and frontal areas (8). Finally, others indicate that perception is associated with a midlatency evoked response (9), the timing of which can be delayed when stimulus energy is decreased to near-threshold levels (10,11).These conflicting findings demonstrate the unresolved nature of the timing underlying visual perception. Moreover, varied interpretations of the term "perception" may contribute to varied interpretations of the neuronal processes being studied, making it more difficult to understand the timing of cognitive events generated by the brain. To avoid such errors in communication, we define the term perception to mean the conscious awareness or detection of a presented visual stimulus: a phenomenon not to be confused with related processes such as visual identification and recognition. Although our definition is limited to the event in which a visual stimulus achieves conscious access, ...

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Section: Methodsmentioning

confidence: 99%

Cortical response tracking the conscious experience of threshold duration visual stimuli indicates visual perception is all or none

Sekar

Findley

Poeppel

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…Prior to any stimulus exposure, subjects were seated in the MSR with the lights turned off for 30 minutes in order to be adequately dark adapted (Barlow, Kohn, & Walsh, 1947). Since stimuli were short (≤ 100 ms) and small (< 1 deg), they were delivered in the dark to optimize the signal to noise ratio of elicited MEG activity.…”

Section: Methodsmentioning

confidence: 99%

Evidence for an all-or-none perceptual response: single-trial analyses of magnetoencephalography signals indicate an abrupt transition between visual perception and its absence

2012

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Whether consciousness is an all-or-none or graded phenomenon is an area of inquiry that has received considerable interest in neuroscience and is as of yet, still debated. In this magnetoencephalography (MEG) study we used a single stimulus paradigm with sub-threshold, threshold and supra-threshold duration inputs to assess whether stimulus perception is continuous with or abruptly differentiated from unconscious stimulus processing in the brain. By grouping epochs according to stimulus identification accuracy and exposure duration, we were able to investigate whether a high-amplitude perception-related cortical event was (1) only evoked for conditions where perception was most probable (2) had invariant amplitude once evoked and (3) was largely absent for conditions where perception was least probable (criteria satisfying an all-on-none hypothesis). We found that averaged evoked responses showed a gradual increase in amplitude with increasing perceptual strength. However, single trial analyses demonstrated that stimulus perception was correlated with an all-or-none response, the temporal precision of which increased systematically as perception transitioned from ambiguous to robust states. Due to poor signal-to-noise resolution of single trial data, whether perception-related responses, whenever present, were invariant in amplitude could not be unambiguously demonstrated. However, our findings strongly suggest that visual perception of simple stimuli is associated with an all-or-none cortical evoked response the temporal precision of which varies as a function of perceptual strength.

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“…The best documented biological effect of dynamic magnetic fields is the induction of visual light flashes known as magnetophosphenes. This phenomenon was first described by D'Arsonval in 1893 and has been studied by other investigators (2,22,51,76,78). In a recent experimental study (23,24), the induction threshold for magnetophosphenes was found to be about 1.3 Tesla per s (rise time = 2 ms) for younger males and about 1.9 Tesla per s for older males (24).…”

Section: Dynamic Magnetic Gradient Fieldsmentioning

confidence: 79%

Safety Aspects of Magnetic Resonance Examinations

Persson

Ståhlberg

1985

Int J Technol Assess Health Care

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In a standard whole-body NMR-scanning machine, the static magnetic field is generated by an electric current driven through large solenoid coils. Dynamic magnetic gradient fields are generated by electric current pulses in coils located at various orientations, thus producing magnetic gradients inx, y, andzdirections. The Rf (radiofrequency) radiation is transmitted through a specially shaped coil which also serves as an antenna receiving the NMR signals.

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The Effect of Dark Adaptation and of Light Upon the Electric Threshold of the Human Eye

Cited by 19 publications

References 0 publications

Cortical response tracking the conscious experience of threshold duration visual stimuli indicates visual perception is all or none

Cortical response tracking the conscious experience of threshold duration visual stimuli indicates visual perception is all or none

Evidence for an all-or-none perceptual response: single-trial analyses of magnetoencephalography signals indicate an abrupt transition between visual perception and its absence

Safety Aspects of Magnetic Resonance Examinations

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