Unconscious processing of invisible visual stimuli

Unconscious processing of subliminal visual information, as illustrated by the above-chance accuracy in discriminating invisible visual stimuli, is evident in both blindsight patients and healthy human observers. However, the dependence of such unconscious processing on stimulus properties remains unclear. Here we studied the impact of stimulus luminance and stimulus complexity on the extent of unconscious processing. A testing stimulus presented to one eye was rendered invisible by a masking stimulus presented to the other eye, and healthy human participants made a forced-choice discrimination of the stimulus identity followed by a report of the perceptual awareness. Without awareness of the stimulus existence, participants could nevertheless reach above-chance accuracy in discriminating the stimulus identity. Importantly, the discrimination accuracy for invisible stimuli increased with the stimulus luminance and decreased with the stimulus complexity. These findings suggested that the input signal strength and the input signal complexity can affect the extent of unconscious processing without altering the subjective awareness

Duality in Binocular Rivalry: Distinct Sensitivity of Percept Sequence and Percept Duration to Imbalance between Monocular Stimuli

Visual perception is usually stable and accurate. However, when the two eyes are simultaneously presented with conflicting stimuli, perception falls into a sequence of spontaneous alternations, switching between one stimulus and the other every few seconds. Known as binocular rivalry, this visual illusion decouples subjective experience from physical stimulation and provides a unique opportunity to study the neural correlates of consciousness. The temporal properties of this alternating perception have been intensively investigated for decades, yet the relationship between two fundamental properties - the sequence of percepts and the duration of each percept - remains largely unexplored

Clinicopathological Significance and Prognostic Value of DNA Methyltransferase 1, 3a, and 3b Expressions in Sporadic Epithelial Ovarian Cancer

Altered DNA methylation of tumor suppressor gene promoters plays a role in human carcinogenesis and DNA methyltransferases (DNMTs) are responsible for it. This study aimed to determine aberrant expression of DNMT1, DNMT3a, and DNMT3b in benign and malignant ovarian tumor tissues for their association with clinicopathological significance and prognostic value. A total of 142 ovarian cancers and 44 benign ovarian tumors were recruited for immunohistochemical analysis of their expression. The data showed that expression of DNMT1, DNMT3a, and DNMT3b was observed in 76 (53.5%), 92 (64.8%) and 79 (55.6%) of 142 cases of ovarian cancer tissues, respectively. Of the serious tumors, DNMT3a protein expression was significantly higher than that in benign tumor samples (P = 0.001); DNMT3b was marginally significant down regulated in ovarian cancers compared to that of the benign tumors (P = 0.054); DNMT1 expression has no statistical difference between ovarian cancers and benign tumor tissues (P = 0.837). Of the mucious tumors, the expression of DNMT3a, DNMT3b, and DNMT1 was not different between malignant and benign tumors. Moreover, DNMT1 expression was associated with DNMT3b expression (P = 0.020, r = 0.195). DNMT1 expression was associated with age of the patients, menopause status, and tumor localization, while DNMT3a expression was associated with histological types and serum CA125 levels and DNMT3b expression was associated with lymph node metastasis. In addition, patients with DNMT1 or DNMT3b expression had a trend of better survival than those with negative expression. Co-expression of DNMT1 and DNMT3b was significantly associated with better overall survival (P = 0.014). The data from this study provided the first evidence for differential expression of DNMTs proteins in ovarian cancer tissues and their associations with clinicopathological and survival data in sporadic ovarian cancer patients

Stimulus-entrained oscillatory activity propagates as waves from area 18 to 17 in cat visual cortex.

Previous studies in cat visual cortex reported that area 18 can actively drive neurons in area 17 through cortico-cortical projections. However, the dynamics of such cortico-cortical interaction remains unclear. Here we used multielectrode arrays to examine the spatiotemporal pattern of neuronal activity in cat visual cortex across the 17/18 border. We found that full-field contrast reversal gratings evoked oscillatory wave activity propagating from area 18 to 17. The wave direction was independent of the grating orientation, and could not be accounted for by the spatial distribution of receptive field latencies, suggesting that the waves are largely mediated by intrinsic connections in the cortex. Different from the evoked waves, spontaneous waves propagated along both directions across the 17/18 border. Together, our results suggest that visual stimulation may enhance the flow of information from area 18 to 17

LFP responses to contrast reversal gratings and frequency analysis of the responses.

<p>(A) Left panel, raw LFP signal from a single channel during a single trial of visual stimulation by 4-Hz contrast reversal grating. Right panel, the black curve is the z-score signal for the trace shown in the left panel, and the red curve is the signal band-pass filtered at 6–10 Hz (2^nd harmonic response). (B) Upper panel, unfiltered LFP signals averaged over all trials in response to a 4-Hz contrast reversal grating (orientation = 135°) for 7 recording sites distributed along the medial-lateral axis. Lower panel, the z-score signal for the responses shown in the upper panel. (C) Power spectra for responses to 4-Hz contrast reversal gratings in all usable channels of the array from one experiment. Log power is presented. (D) Spatial coherence as a function of frequency computed from a space-frequency SVD analysis, averaged over 10 experiments. Shaded region: standard error of the mean.</p

Comparison of the gradient between 2^nd harmonic phase map and RF latency map.

<p>(A) Upper, phase maps computed from the 2^nd harmonic responses of two experiments measured with 4-Hz contrast reversal gratings. Lower, RF latency maps measured in the same two experiments. Broken channels were marked with ‘*’. (B) Gradient directionality of the phase map was significantly larger than that of the RF latency map (P<0.01, n = 10, Wilcoxon signed rank test).</p

Waves in single-trial responses and evoked responses to 4-Hz contrast reversal gratings.

<p>(A) Left, schematic drawing of areas 17 and 18 (right hemisphere) and the recording sites of the 8×8 array. A, anterior; P, posterior; L, lateral; M, medial. Middle, Single-trial LFPs band-pass filtered at 6–10 Hz during one cycle of oscillation for the 7 recording sites indicated in the left panel. Each red circle marks the trough of response in each site. Right, phase map obtained by averaging the instantaneous phases over the time points within one cycle of oscillation shown in the middle panel for each recording site across the array. Broken channels were marked with ‘*’. Since the electrodes on the rightmost column of the array were not properly inserted into the cortex because the electrodes were near the lateral sulcus, only 8×7 of the recording sites were used for the analysis. (B) Left, time snapshots of two wave-like events from single-trial responses. The data for the first event was the same as those shown in (A). Right, two phase maps for the two wave-like events, respectively. The phase data were interpolated for display purpose. (C) Responses averaged over all trials (i.e., evoked responses) for the 7 recording sites indicated in the left panel of (A). Systematic phase shift can be observed in every cycle of the responses. (D) Left, snapshots of 2 cycles of evoked responses measured from one experiment in the right hemisphere. Upper right, a phase map computed by the method of Hilbert transform, Lower right, a phase map containing the phase of 2^nd harmonic component computed by Fourier analysis. The two phase maps were computed from the same data set. Data were interpolated for display purpose.</p

Schematic depiction of binocular rivalry and experimental paradigms.

<p>(A) To induce binocular rivalry, a pair of orthogonal gratings (tilted +45° and −45° away from the vertical) were separately presented to the two eyes of the human subjects, and subjects experienced the alternating dominance between one grating and the other. Between the stimulus onset and the first percept, there existed a short period during which subjects experienced the fusion of the two gratings, rather than the complete dominance of one grating over the other. (B) and (C) To measure the first percept and its latency, rivalry stimuli were briefly presented for a duration varied from 10 msec to 500 msec, and subjects reported their perception through a three-alternative forced choice (+45° grating, the −45° grating, or the fusion of two gratings). The trails in which subjects reported the fusion perception were taken into account only when we calcualted the latency of the first percept, and different conditions of stimulus duration were combined in the analyses except for calculating this latency.</p