Crowding by Invisible Flankers

Abstract Background: Human object recognition degrades sharply as the target object moves from central vision into peripheral vision. In particular, one's ability to recognize a peripheral target is severely impaired by the presence of flanking objects, a phenomenon known as visual crowding. Recent studies on how visual awareness of flanker existence influences crowding had shown mixed results. More importantly, it is not known whether conscious awareness of the existence of both the target and flankers are necessary for crowding to occur

Responsiveness of the EuroQoL 5-Dimension (EQ-5D) questionnaire in patients with spondyloarthritis.

BACKGROUND: Spondyloarthritis (SpA) has a significant impact on patients' quality of life due to functional impairments. Generic health instruments like the EuroQoL 5-dimension (EQ-5D) is important for cost-utility analysis of health care interventions and calculation of quality-adjusted life-years. It has been validated in patients with SpA. However, its responsiveness property is unclear. Hence, the aim of study is to test the responsiveness properties of the EQ-5D health measure for Chinese patients with SpA. METHODS: Prospective and consecutive recruitment of 151 Chinese patients with SpA was conducted with follow-up assessments 6 months later. Demographic data including smoking and drinking habits, education level, income and occupation was collected. Disease-associated data including disease duration, presence of back pain, peripheral arthritis, dactylitis, enthesitis, uveitis, psoriasis, and inflammatory bowel disease was also recorded. Questionnaires regarding disease activity and functional disability (BASDAI, BASFI, BASGI, BASMI, ASDAS), mental health (HADS) and the EQ-5D scores were recorded. Responsiveness was tested against the global rating of change scale (GRC) and changes in disease activity using BASDAI and ASDAS-CRP. RESULTS: A total of 113 (74.8%) patients completed the follow-up assessments. Most patients (61.6%) had low disease activity level with BASDAI <4 and 39.7% of patients had inactive disease by ASDAS-CRP. EQ-5D scores was well discriminated along with BASDAI and BASFI scores. EQ-5D scores also correlated well with HADS. The GRC was not able to discriminate adequately. No significant ceiling or floor effect was observed. CONCLUSIONS: EQ-5D demonstrates satisfactory responsiveness property for assessment of changes in SpA disease activity. LEVEL OF EVIDENCE: II

Crowding by Invisible Flankers

BACKGROUND: Human object recognition degrades sharply as the target object moves from central vision into peripheral vision. In particular, one's ability to recognize a peripheral target is severely impaired by the presence of flanking objects, a phenomenon known as visual crowding. Recent studies on how visual awareness of flanker existence influences crowding had shown mixed results. More importantly, it is not known whether conscious awareness of the existence of both the target and flankers are necessary for crowding to occur. METHODOLOGY/PRINCIPAL FINDINGS: Here we show that crowding persists even when people are completely unaware of the flankers, which are rendered invisible through the continuous flash suppression technique. Contrast threshold for identifying the orientation of a grating pattern was elevated in the flanked condition, even when the subjects reported that they were unaware of the perceptually suppressed flankers. Moreover, we find that orientation-specific adaptation is attenuated by flankers even when both the target and flankers are invisible. CONCLUSIONS: These findings complement the suggested correlation between crowding and visual awareness. What's more, our results demonstrate that conscious awareness and attention are not prerequisite for crowding

Crowding of Upright Chinese Character is Stronger with Inverted than Upright Flankers: An Exception of the Similarity Rule

Upright flanking faces have stronger detrimental effects on the recognition of upright target face, than inverted flanking faces. One possible explanation for this “flanker- inversion effect” was that the more holistically processed upright flanking faces allowed for more erroneous feature integration. Alternatively, crowding was known to be stronger when target and flankers were more similar. Here we investigate flanker-inversion effect on crowding in Chinese character identification. Five normally-sighted young adults participated. Targets of size 1.2° were presented at 5° in the lower visual field. Four flankers with center-to-center distance of 1.8° were presented in the crowded condition. Three types of flankers were used, upright or inverted Chinese and upright Korean characters. The identification contrast thresholds were estimated by QUEST and crowding strength was measured through threshold elevation (TE). Crowding on upright Chinese target was significantly stronger with inverted Chinese flankers (TE = 1.59±0.32) than with upright Chinese flankers (TE = 1.47±0.29). No inversion effect was observed for inverted Chinese target. Korean flankers produced similar crowding as upright Chinese flankers. Our results go against the similarity rule that predicts upright Chinese flankers would produce stronger crowding for upright Chinese target. Holistic processing preferred for inverted Chinese characters may account for the findings

P2-36: Spatial Frequency Characteristics of Chinese Character Recognition in Different Complexity Categories

Objective: Human visual system is able to recognize objects in large complexity variation. Despite such capability, little is known about the effects of complexity on object recognition. Here we studied the spatial frequency (SF) characteristics in identifying Chinese characters (CCs) of different complexity levels. Method: Stimuli were 150 frequently used CCs categorized into 3 complexity groups. Each character was digitally band-passed by 11 cosine log filters (bandwidth = 2 octaves, center frequency = 1.27 to 12.8 cycles/character in 0.1 log step). We measured contrast sensitivity for recognizing CCs of sizes 0.5°, 1°, and 2°. Peak SF (cycles/deg) and bandwidth (octaves) were plotted against character size in nominal character frequency (cycles/deg). A CSF ideal observer model (Chung et al., 2002 Vision Research 42 2137–2152) was formulated to examine whether early CSF filtering followed by template matching could explain human performance. Results: Log-log slopes of peak SF vs. size functions were 0.60±0.04 (M±SD), 0.67±0.02, and 0.72±0.05 for the low, medium, and high complexity groups. Bandwidth of the tuning functions was approximately 2 octaves for all complexity groups. Preliminary results from the CSF ideal observer analysis showed shallower slopes for the peak SF vs. size functions, but a similar trend for the bandwidth data compared with human performance. Conclusions: Peak SF of the tuning function did not scale perfectly with character size (log-log slopes < 1). The SF characteristics of CC recognition exhibited size-dependence, which differed across complexity groups. The ideal observer model utilizing human CSF and character-identity information failed to explain our data

Results from the critical spacing experiment.

<p>(A) Individual observer data. Contrast thresholds (in log scale) for identifying target grating patterns presented in various degrees of eccentricity as a function of center-to-center distance between the target and flanking gratings. Error bars indicate the standard deviations (3 data points per condition was collected from each observer). Stimuli presented in this experiment were identical to those used previously in the CFS trials of the grating orientation discrimination experiment (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028814#pone-0028814-g001" target="_blank">Figure 1A</a>). (B) The critical spacing of crowding (in degree) as a function of eccentricity (n = 2). Bouma's proportionality constant <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028814#pone.0028814-Mudrik1" target="_blank">[23]</a> is illustrated here for reference.</p

Results from the grating orientation discrimination experiment.

<p>(A) Stimuli presented in the experiment. In the CFS trials, flanking stimuli presented to the non-dominant eye of the observers in the flanked condition were perceptually suppressed from awareness by the CFS stimuli that were simultaneously presented to their dominant eye. Thus, in any given CFS trial, only the target grating pattern and the CFS stimuli were perceptually visible. Note that the actual contrast of the stimuli presented to their non-dominant eye was much lower than that illustrated here. (B) Contrast thresholds (in log scale) in the unflanked and flanked conditions as a function of CFS (n = 4). Error bars indicate the standard errors of the means.</p

Illusory contour formation survives crowding

Flanked objects are difficult to identify using peripheral vision due to visual crowding, which limits conscious access to target identity. Nonetheless, certain types of visual information have been shown to survive crowding. Such resilience to crowding provides valuable information about the underlying neural mechanism of crowding. Here we ask whether illusory contour formation survives crowding of the inducers. We manipulated the presence of illusory contours through the (mis)alignment of the four inducers of a Kanizsa square. In the inducer-aligned condition, the observers judged the perceived shape (thin vs. fat) of the illusory Kanizsa square, manipulated by small rotations of the inducers. In the inducer-misaligned condition, three of the four inducers (all except the upper-left) were rotated 908. The observers judged the orientation of the upper-left inducer. Crowding of the inducers worsened observers&apos; performance significantly only in the inducer-misaligned condition. Our findings suggest that information for illusory contour formation survives crowding of the inducers. Crowding happens at a stage where the low-level featural information is integrated for inducer orientation discrimination, but not at a stage where the same information is used for illusory contour formation