Flash Suppression Research Articles

Attentional scope modulates unconscious processing: evidence from breaking continuous flash suppression

Attentional scope modulates unconscious processing: evidence from breaking continuous flash suppression

Neuronal correlates of binocular rivalry in the human medial temporal lobe

Firing of neurons in the human medial temporal lobe (MTL) was shown to correlate with conscious perception both using flash suppression (Kreiman et al 2002) and backward masking (Quiroga et al 2008). However, in both of these paradigms, perception was externally manipulated rather than internally driven. Thus, it remains unclear whether MTL neurons are involved in internally generating the percept, or only follow it. Here we used binocular rivalry, where perceptual switches are internally driven, in epilepsy patients implanted with depth electrodes (for clinical purpose). Based on a conventional screening paradigm, pairs of images that elicited selective responses were presented binocularly. Patients were asked to report perceptual transitions by pressing and releasing two buttons. These reports were then used to create a replay condition. We found that neurons in the MTL responded up to 1000ms before patients released the button to indicate the initiation of a perceptual switch (i.e. piecemeal period) to the cells’ preferred image. This was found both for cells that expressed selectivity by increasing or by decreasing their firing rate in response to their preferred stimulus. Even after accounting for motor reaction time, these neuronal responses are still quite early, especially considering that MTL neuronal response time is typically 300-400ms after stimulus presentation. It appears that neurons in different areas responded with different times relative to the behavioral report of the perceptual switch, with the amygdala generating some of the earliest responses. Importantly, the neuronal response was earlier in the rivalry condition as compared to the replay condition. Our results suggest that MTL neurons are not merely reflecting but likely take part in the process leading to conscious perception or to a switch in perception. Meeting abstract presented at VSS 2013

Posing for awareness: Proprioception modulates access to visual consciousness in a continuous flash suppression task

Posing for awareness: Proprioception modulates access to visual consciousness in a continuous flash suppression task

The function of consciousness in multisensory integration

The function of consciousness was explored in two contexts of audio–visual speech, cross-modal visual attention guidance and McGurk cross-modal integration. Experiments 1, 2, and 3 utilized a novel cueing paradigm in which two different flash suppressed lip-streams cooccured with speech sounds matching one of these streams. A visual target was then presented at either the audio-visually congruent or incongruent location. Target recognition differed for the congruent versus incongruent trials, and the nature of this difference depended on the probabilities of a target appearing at these respective locations. Thus, even though the lip-streams were never consciously perceived, they were nevertheless meaningfully integrated with the consciously perceived sounds, and participants learned to guide their attention according to statistical regularities between targets and these unconsciously perceived cross-modal cues. In Experiment 4, McGurk stimuli were presented in which the lip-streams were either flash suppressed (4a) or unsuppressed (4b), and the McGurk effect was found to vanish under conditions of flash suppression. Overall, these results suggest a simple yet fundamental principle regarding the function of consciousness in multisensory integration – cross-modal effects can occur in the absence of consciousness, but the influencing modality must be consciously perceived for its information to cross modalities.

Letter perception under binocular rivalry by flash suppression

Letter perception under binocular rivalry by flash suppression

Subjective discriminability of invisibility: A framework for distinguishing perceptual and attentional failures of awareness

Conscious visual perception can fail in many circumstances. However, little is known about the causes and processes leading to failures of visual awareness. In this study, we introduce a new signal detection measure termed subjective discriminability of invisibility (SDI) that allows one to distinguish between subjective blindness due to reduction of sensory signals or to lack of attentional access to sensory signals. The SDI is computed based upon subjective confidence in reporting the absence of a target (i.e., miss and correct rejection trials). Using this new measure, we found that target misses were subjectively indistinguishable from physical absence when contrast reduction, backward masking and flash suppression were used, whereas confidence was appropriately modulated when dual task, attentional blink and spatial uncertainty methods were employed. These results show that failure of visual perception can be identified as either a result of perceptual or attentional blindness depending on the circumstances under which visual awareness was impaired.

Single neuron responses in humans during binocular rivalry and flash suppression

Single neuron responses in humans during binocular rivalry and flash suppression

Ultrasonic signal processor for a hand held ultrasonic diagnostic instrument

A hand held ultrasonic instrument is provided in a portable unit which performs both B mode and Doppler imaging. The instrument includes a transducer array mounted in a hand-held enclosure, with an integrated circuit transceiver connected to the elements of the array for the reception of echo signals. A digital signal processing circuit performs both B mode and Doppler signal processing such as filtering, detection and Doppler estimation, as well as advanced functions such as assembly of multiple zone focused scanlines, synthetic aperture formation, depth dependent filtering, speckle reduction, flash suppression, and frame averaging.

Inter-ocular contrast normalization in human visual cortex

The brain combines visual information from the two eyes and forms a coherent percept, even when inputs to the eyes are different. However, it is not clear how inputs from the two eyes are combined in visual cortex. We measured fMRI responses to single gratings presented monocularly, or pairs of gratings presented monocularly or dichoptically with several combinations of contrasts. Gratings had either the same orientation or orthogonal orientations (i.e., plaids). Observers performed a demanding task at fixation to minimize top-down modulation of the stimulus-evoked responses. Dichoptic presentation of compatible gratings (same orientation) evoked greater activity than monocular presentation of a single grating only when contrast was low (<10%). A model that assumes linear summation of activity from each eye failed to explain binocular responses at 10% contrast or higher. However, a model with binocular contrast normalization, such that activity from each eye reduced the gain for the other eye, fitted the results very well. Dichoptic presentation of orthogonal gratings evoked greater activity than monocular presentation of a single grating for all contrasts. However, activity evoked by dichoptic plaids was equal to that evoked by monocular plaids. Introducing an onset asynchrony (stimulating one eye 500 ms before the other, which under attentive vision results in flash suppression) had no impact on the results; the responses to dichoptic and monocular plaids were again equal. We conclude that when attention is diverted, inter-ocular suppression in V1 can be explained by a normalization model in which the mutual suppression between orthogonal orientations does not depend on the eye of origin, nor on the onset times, and cross-orientation suppression is weaker than inter-ocular (same orientation) suppression.

Effect of transient versus sustained activation on interocular suppression

Switches in perceptual dominance resulting from either binocular rivalry or flash suppression likely involve some mechanism of interocular suppression, although it is unclear from past research whether different mechanisms are involved in the two cases. Using monocular, centrally fixated sinusoidal gratings surrounded by contiguous annuli of rivalrous gratings, suppression of the entire central grating was possible using either technique. However, the magnitude of the suppression was unaffected by the presence of an ipsilateral surround for flash suppression, yet, for binocular rivalry, suppression no longer occurred when the surrounds were fusible. Nevertheless, computational modeling demonstrates that the differences between the techniques may be attributable to the sustained versus transient stimulation of the contralateral surround, with the magnitude of the suppression proportional to the activation of the contralateral surround. Consistent with this, suppression extends over a greater distance at the onset of the contralateral surround than during sustained rivalry. Therefore, it is likely that perceptual dominance in both binocular rivalry and flash suppression is based on the same mechanism of interocular suppression.

Depth of interocular suppression associated with continuous flash suppression, flash suppression, and binocular rivalry

When conflicting images are presented to the corresponding regions of the two eyes, only one image may be consciously perceived. In binocular rivalry (BR), two images alternate in phenomenal visibility; even a salient image is eventually suppressed by an image of low saliency. Recently, N. Tsuchiya and C. Koch (2005) reported a technique called continuous flash suppression (CFS), extending the suppression duration more than 10-fold. Here, we investigated the depth of this prolonged form of interocular suppression as well as conventional BR and flash suppression (FS) using a probe detection task. Compared to monocular viewing condition, CFS elevated detection thresholds more than 20-fold, whereas BR did so by 3-fold. In subsequent experiments, we dissected CFS into several components. By manipulating the number and timing of flashes with respect to the probe, we found that the stronger suppression in CFS is not due to summation between BR and FS but is caused by the summation of the suppression due to multiple flashes. Our results support the view that CFS is not a stronger version of BR but is due to the accumulated suppressive effects of multiple flashes.

Ultrasonic signal processor for power Doppler imaging in a hand held ultrasonic diagnostic instrument

A hand held ultrasonic instrument is provided in a portable unit which performs both B mode and Doppler imaging. The instrument includes a transducer array mounted in a hand-held enclosure, with an integrated circuit transceiver connected to the elements of the array for the reception of echo signals. A digital signal processing circuit performs both B mode and Doppler signal processing such as filtering including wall filtering matrix and Hartley transform matrix functions, detection and Doppler estimation, as well as advanced functions such as assembly of multiple zone focused scanlines, synthetic aperture formation, depth dependent filtering, speckle reduction, flash suppression, and frame averaging. The advent of color flow imaging based on Doppler frequency estimation in medical ultrasound addresses a need for rapid assessment of overall flow characteristics in cardiac care. Typical prior art implementation utilize a high degree of temporal filtering in order to enhance the flow signal, but makes the image slow to respond to changes in flow. This is true of both directional and non-directional implementations, and is necessitated by the instability of traditional estimation techniques that are derived from older color flow techniques. A significant advantage of the present invention is excellent stability of both power and direction estimates.

Adjustable temperature cryostat for optical studies

Switches in perceptual dominance resulting from either binocular rivalry or flash suppression likely involve some mechanism of interocular suppression, although it is unclear from past research whether different mechanisms are involved in the two cases. Using monocular, centrally fixated sinusoidal gratings surrounded by contiguous annuli of rivalrous gratings, suppression of the entire central grating was possible using either technique. However, the magnitude of the suppression was unaffected by the presence of an ipsilateral surround for flash suppression, yet, for binocular rivalry, suppression no longer occurred when the surrounds were fusible. Nevertheless, computational modeling demonstrates that the differences between the techniques may be attributable to the sustained versus transient stimulation of the contralateral surround, with the magnitude of the suppression proportional to the activation of the contralateral surround. Consistent with this, suppression extends over a greater distance at the onset of the contralateral surround than during sustained rivalry. Therefore, it is likely that perceptual dominance in both binocular rivalry and flash suppression is based on the same mechanism of interocular suppression.