Direction biasing by brief apparent motion stimuli

The perceived direction of a motion step (probe stimulus) can be influenced by an earlier motion step or a brief motion sweep containing a series of steps (biasing stimulus). Depending upon experimental conditions, the biasing of the direction of the probe step (a phase shift of 180 degrees +/- Phi) by a biasing stimulus which precedes it by approximately 250 ms can either increase (positive filter biasing) or decrease (negative filter biasing) the tendency to see the probe move: in the biasing direction as computed with a motion filter with a biphasic temporal impulse response. In a series of experiments it was found that biasing motions traversing 90 degrees of phase angle in fewer than six steps in less than 100 ms produced positive filter biasing. Also, biasing of the probe direction could be dissociated from the consciously reported direction of the biasing stimulus, and it did not occur when the probe preceded rather than followed the biasing stimulus. A biasing sweep containing more than six steps traversing 90 degrees or a sweep traversing 270 degrees produced negative filter biasing. Perceptual fusion of the steps of the sweep was not a necessary condition for obtaining negative filter biasing. In general, the negative filter biasing effects were found to be the: most pervasive for the conditions investigated, and they are suggestive of a direction-specific, adaptation-like (gain-control) process in first-order motion filters. The exception to the negative biasing rule was found only with biasing stimuli which were short in duration or distance spanned. (C) 2000 Elsevier Science Ltd. All rights reserved

On the effectiveness of noise masks: Naturalistic vs. un-naturalistic image statistics

AbstractIt has been argued that the human visual system is optimized for identification of broadband objects embedded in stimuli possessing orientation averaged power spectra fall-offs that obey the 1/fβ relationship typically observed in natural scene imagery (i.e., β=2.0 on logarithmic axes). Here, we were interested in whether individual spatial channels leading to recognition are functionally optimized for narrowband targets when masked by noise possessing naturalistic image statistics (β=2.0). The current study therefore explores the impact of variable β noise masks on the identification of narrowband target stimuli ranging in spatial complexity, while simultaneously controlling for physical or perceived differences between the masks. The results show that β=2.0 noise masks produce the largest identification thresholds regardless of target complexity, and thus do not seem to yield functionally optimized channel processing. The differential masking effects are discussed in the context of contrast gain control

Contrast Adaptation Contributes to Contrast-Invariance of Orientation Tuning of Primate V1 Cells

BACKGROUND: Studies in rodents and carnivores have shown that orientation tuning width of single neurons does not change when stimulus contrast is modified. However, in these studies, stimuli were presented for a relatively long duration (e. g., 4 seconds), making it possible that contrast adaptation contributed to contrast-invariance of orientation tuning. Our first purpose was to determine, in marmoset area V1, whether orientation tuning is still contrast-invariant with the stimulation duration is comparable to that of a visual fixation. METHODOLOGY/PRINCIPAL FINDINGS: We performed extracellular recordings and examined orientation tuning of single-units using static sine-wave gratings that were flashed for 200 msec. Sixteen orientations and three contrast levels, representing low, medium and high values in the range of effective contrasts for each neuron, were randomly intermixed. Contrast adaptation being a slow phenomenon, cells did not have enough time to adapt to each contrast individually. With this stimulation protocol, we found that the tuning width obtained at intermediate contrast was reduced to 89% (median), and that at low contrast to 76%, of that obtained at high contrast. Therefore, when probed with briefly flashed stimuli, orientation tuning is not contrast-invariant in marmoset V1. Our second purpose was to determine whether contrast adaptation contributes to contrast-invariance of orientation tuning. Stationary gratings were presented, as previously, for 200 msec with randomly varying orientations, but the contrast was kept constant within stimulation blocks lasting >20 sec, allowing for adaptation to the single contrast in use. In these conditions, tuning widths obtained at low contrast were still significantly less than at high contrast (median 85%). However, tuning widths obtained with medium and high contrast stimuli no longer differed significantly. CONCLUSIONS/SIGNIFICANCE: Orientation tuning does not appear to be contrast-invariant when briefly flashed stimuli vary in both contrast and orientation, but contrast adaptation partially restores contrast-invariance of orientation tuning

Direction-specific changes of sensitivity after brief apparent motion stimuli

AbstractDirection-specific losses in sensitivity were found for a test grating which was superimposed on a stationary contrast pedestal and which moved either in the same or opposite direction as a prior biasing stimulus. Three types of biasing stimuli were employed: a grating swept through 270° in 45° steps, a single 90° step of a grating, and a single 90° step of a grating which contained a blank IFI and whose perceived direction was reversed. For the biasing sweep and the single 90° step, the response of directionally selective mechanisms (directional motion energy) is greatest for the direction which corresponds to the actual physical displacement of the stimulus. For the biasing step with an IFI, the response is maximum for the opposite direction. For all three types of biasing stimuli, directional sensitivity for a test stimulus was reduced most when it moved in the biasing direction, i.e. the direction which produced the strongest signal in directionally selective mechanisms. Unlike the effects of the same types of biasing stimuli on the perceived direction of a suprathreshold 180° step of a grating [Pinkus, A., & Pantle, A. (1997). Probing motion signals with a priming paradigm. Vision Research, 37, 541–52; Pantle, A., Gallogly, D.P., & Piehler, O.C. (2000). Direction biasing by brief apparent motion stimuli. Vision Research, 40, 1979–91], all the direction-specific losses of sensitivity can be explained by changes in the response characteristics of directionally selective mechanisms

A statewide approach to systematising hand hygiene behaviour in hospitals : clean hands save lives, part I

OBJECTIVE: To describe the planning and execution of a statewide campaign aimed at improving compliance with hand hygiene practices in New South Wales public hospitals. DESIGN AND SETTING: The campaign was conducted in all area health services (AHSs) in NSW (covering 208 public hospitals) between February 2006 and February 2007. Clinical practice improvement methods and campaign strategies were used to improve the availability and use of alcohol-based hand rub (AHR) at the point of patient care, using staff champions and local leaders, engaging patients and families, and measuring compliance. Staff were given regular feedback on their performance. Project officers funded by the Clinical Excellence Commission (CEC) provided local project management support and implemented the campaign in a standardised format orchestrated by the CEC. MAIN OUTCOME MEASURES: Proportion of available beds with secured and unsecured AHR containers nearby; amount of AHR used (based on purchasing patterns). RESULTS: Hospital visits before the campaign identified a lack of appropriately placed AHR at the point of care. The number of AHR containers per available bed in near-patient locations increased to 13 280/18 951 (70%) after the campaign. The quantity of AHR purchased per month across NSW public hospitals increased from 1477 L to 5568 L (a 377% increase). CONCLUSION: The CEC was successful in systematising the placement of AHR in all NSW public hospitals at the point of patient care. Although the use of AHR increased substantially, some staff were resistant to changing their hand hygiene practices.5 page(s

Improvements in hand hygiene across New South Wales public hospitals : clean hands save lives, part III

OBJECTIVE: To describe improvements in hand hygiene compliance after a statewide hand hygiene campaign conducted in New South Wales public hospitals. DESIGN AND SETTING: The campaign was conducted in all area health services in NSW (covering all 208 public hospitals). Alcohol-based hand rub (AHR) was introduced into all hospitals between March and June 2006. In each hospital, five overt observation surveys of hand hygiene compliance by health care workers (HCWs) were conducted: one pre-implementation survey and four post-implementation surveys (in August 2006, November 2006, February 2007 and July 2008). MAIN OUTCOME MEASURES: Overtly observed hand hygiene compliance rates by HCWs, stratified by before- and after-patient contact, Fulkerson's contact risk categories, and four health care professional groupings. RESULTS: The overall hand hygiene compliance rate improved from 47% before the intervention to an average of 61% over the last three observation periods (P < 0.001). All professional groups sustained improved compliance rates except medical staff, whose practices reverted to pre-intervention rates. Nursing staff maintained significantly improved compliance, with an average rate of 67% after the intervention. Overall hand hygiene compliance before patient contact improved from 39% (pre-campaign) to 52% (July 2008) (P < 0.001). Overall compliance after patient contact improved from 57% to 64% (P < 0.001) over the same period. Compliance associated with medium-risk contacts increased from an average of 51% in the first two observation periods to an average of 62% over the last three observation periods (P < 0.001). The corresponding compliance rates associated with low-risk contacts were 35% and 56%, respectively (P < 0.001). CONCLUSION: An overall improvement in hand hygiene rates was achieved with the introduction of AHR. Increased adherence to before-patient contact compliance, especially by nursing staff, contributed to the progress made, but an acceptable overall level of hand hygiene practice is yet to be achieved. It is now time to focus on a long-term behavioural change program directed specifically at medical staff.7 page(s

Culture change for hand hygiene : clean hands save lives, part II

OBJECTIVE: To present the results of surveys of staff, patients and visitors about their perceptions of hand hygiene behaviour before and after implementation of the Clean hands save lives campaign in New South Wales public hospitals. DESIGN AND SETTING: Pre- and post-campaign questionnaires, disseminated through project officers in each health authority, were completed by selected staff and patients/visitors in all 208 public hospitals in NSW. Combined, de-identified results for each health authority were forwarded to the NSW Clinical Excellence Commission for analysis. MAIN OUTCOME MEASURES: Awareness of campaign material; staff perceptions about their ability to maintain a high level of hand hygiene compliance before and after contact with patients; compliance self-reported by staff compared with compliance perceived by patients/visitors and compliance assessed by overt observation. RESULTS: Most staff and patients/visitors were aware of campaign materials. Eighty-six per cent of staff respondents (495/578) believed that placement of alcohol-based hand rub (AHR) close to the point of patient care had improved hand hygiene compliance, and 76% (510/671) believed they could sustain their level of compliance. Only 1 in 4 patients or visitors (106/397) were willing to question health care workers who appeared not to be complying with hand hygiene practices. CONCLUSION: As the first coordinated statewide campaign to modify hand hygiene culture, the Clean hands save lives campaign successfully engendered positive attitudes and dispelled negative perceptions about the onerous nature of before- and after-patient-contact hand hygiene compliance.5 page(s