Teamwork behaviours and errors during neonatal resuscitation.

OBJECTIVE: To describe relationships between teamwork behaviours and errors during neonatal resuscitation. METHODS: Trained observers viewed video recordings of neonatal resuscitations (n = 12) for the occurrence of teamwork behaviours and errors. Teamwork state behaviours (such as vigilance and workload management, which extend for some duration) were assessed as the percentage of each resuscitation that the behaviour was observed and correlated with the percentage of observed errors. Teamwork event behaviours (such as information sharing, inquiry and assertion, which occur at specific times) were counted in 20-s intervals before and after resuscitation steps, and a generalised linear mixed model was calculated to evaluate relationships between these behaviours and errors. RESULTS: Resuscitation teams who were more vigilant committed fewer errors (Spearman's rho for vigilance and errors = -0.62, 95% CI -0.07 to -0.87, p = 0.031). Assertions were more likely to occur before errors than correct steps (OR = 1.44, 95% CI 1.10 to 1.89, p = 0.008) and teaching/advising occurred less frequently after errors (OR = 0.59, 95% CI 0.37 to 0.94, p = 0.028). Though not statistically significant, there was less information sharing before errors (OR = 0.90, 95% CI 0.77 to 1.05, p = 0.172). CONCLUSIONS: Vigilance is an important behaviour for error management. Assertion may have caused errors, or perhaps was an indicator for some other factor that caused errors. Teams may have preferred to resolve errors directly, rather than using errors as opportunities to teach their teammates. These observations raise important questions about the appropriate use of some teamwork behaviours and how to include them in team training programmes.

Asymmetries in contrast polarity processing in young human infants.

Luminance increments and decrements of equal magnitude are processed asymmetrically in the adult visual system. At detection threshold, decrements are slightly easier to detect than increments. At suprathreshold contrast levels decrements appear to have more contrast than increments when both differ from the background by the same absolute amount. Two experiments are reported with 3.5-month-old human infants examining the processing of luminance increments and decrements. Using two different methods to measure the relative salience of positive and negative polarity high contrast bars, we found consistent evidence that dark bars appeared more salient to infants than light bars when both differed from the background by the same absolute amount. The asymmetry may be explained by noting that when luminance increments and decrements have the same Weber contrast, the decrements will have greater Michelson contrast. Perceived contrast in adults follows Michelson contrast more closely than Weber contrast, and a similar metric may characterize the relations between negative and positive contrasts in young human infants.

Contrast discrimination under temporally varying contrast conditions.

Psychophysical contrast discrimination of a 0.8-cpd vertical grating was tested using a paradigm that alternated test and masking gratings at 8 Hz. Masking contrasts were lower than, equal to, or higher than the test contrasts. Six test contrasts were combined factorially with six masking contrasts to generate a series of six contrast increment threshold versus test contrast curves (tvc curves). A particularly simple relationship existed between these curves. The curves could be brought into alignment by shifting them diagonally by the ratio of their masking contrasts. It is shown that this behavior is predicted by a model in which contrast gain is set by the average of the test and masking contrasts coupled with a simple model of contrast discrimination. Contrast gain control integrates contrast over a period of at least 125 msec, and contrast discrimination is a function of this time-averaged contrast.

Competition in early exogenous orienting between 7 and 21 weeks.

Exogenous (stimulus-driven) orienting between 7 and 21 weeks of age was examined in 2 experiments using a display with multiple potential targets of attention. On each trial a small moving probe was used to draw attention to one side of the display or the other. This moving probe appeared simultaneously with 27 static bars. In the first experiment, sensitivity to the moving target was affected significantly by the spatial distribution of these red and green static bars for 14-week-olds but not for 8-week-olds. Sensitivity to the moving target was lower for 14-week-olds when most of the red bars appeared contralaterally to the moving target. This effect replicated a similar effect observed in J. L. Dannemiller (1998). The lack of a contralateral competition effect in Experiment 1 for the 8-week-olds may have occurred because I used a stronger motion stimulus for the younger infants in an attempt to hold the overall performance constant at the 2 ages. A second experiment using a weaker motion stimulus showed that this contralateral competition effect was observable over the entire age range from 7 to 21 weeks of age. Thus as early as 7 weeks of age, sensitivity for a small moving stimulus can be significantly influenced by the simultaneous presence of competing targets of attention in the visual field. Large increases in overall sensitivity were also found across the age range from 7 to 21 weeks. Results are discussed in terms of the development of putative competition mechanisms involved in exogenous orienting.

Contrast gain control in psychophysical contrast discrimination.

Contrast masking may in part reflect the operation of contrast gain control mechanisms in the visual system. Four experiments were conducted in order to examine contrast discrimination under conditions in which the base contrast was interrupted with various maskers. Interrupting the base contrast grating at 8 Hz--with a uniform field, with a randomly phase-shifted version of the same grating, or with a higher contrast version of the same grating--interfered with contrast discrimination. These effects occurred only when the background contrast was above its own threshold. These results may be explained by assuming that the networks responsible for contrast gain control operate by temporally averaging contrast over a period greater than 62.5 msec. When this time-averaged contrast is different from the base contrast, contrast discrimination suffers.

Temporal modulation enhances the efficiency of spatial offset discriminations by 6-month-olds.

Fourteen- and 24-week-old infants were tested for sensitivity to small position differences under two conditions: (a) the Vernier stimulus was flashed on and off at 1.2 or 4.8 Hz (flash condition); and (b) the Vernier breaks were presented in apparent motion at 1.2 or 4.8 Hz (motion condition). The latter stimulus also contained local flicker cues. Each infant was tested at one temporal frequency with both stimuli. No benefit was shown by 14-week-olds at either temporal frequency from the additional motion and flicker cues. However, 24-week-olds required spatial offsets only one third as large in the motion condition as they required in the flash condition at 4.8 Hz. Ideal observer methodology was used to ensure that the spatial information for both of these discriminations was held strictly equivalent. Increasing sensitivity to flicker and/or motion or uncertainty reduction may underlie the enhancement in discrimination shown by 24-week-olds at 4.8 Hz.

A competition model of exogenous orienting in 3.5-month-old infants.

Four experiments are reported on exogenous (stimulus-driven) orienting in 3.5-month-old infants. A small moving bar embedded in a field of static bars was used to draw the infant's attention to one side of the display or the other. The bars could be either red or green. In all four of these experiments sensitivity to this small moving bar was affected significantly by how unevenly the red and green bars were distributed across the visual field. Sensitivity to the moving bar was lower when most of the red bars were in the field contralateral to this probe suggesting competition between the motion stimulus and contralaterally placed red but not green bars on a small, but significant proportion of trials. This basic effect replicated in four separate experiments and depended coarsely on how unevenly the red and the green bars were distributed across the field. A competition model of exogenous orienting with a winner-take-all rule captured the most important features of the data. The distribution of color within the visual field can bias attention significantly at 3.5 months making it either more or less likely that an infant will detect a moving stimulus.

Spatial sampling of motion: seeing an object moving behind a picket fence.

Spatially sampled motion (H.P. Snippe & J.J. Koenderink, 1994) leads to time-lagged correlations of luminance change at discrete spatial positions. Observers matched the perceived width of a bar whose motion path was sampled spatially to the width of a static bar; the width of the moving object was not directly observable. Observers did reasonably well on this task when the stimulus onset asynchrony (SOA) between adjacent samples was approximately 90 ms, but performance broke down completely when the SOA was doubled. Performance improved considerably as more samples became available, provided that these samples all fell along the same smooth motion path and were seen by the same eye. This spatiotemporal information in spatially sampled motion can specify the width of a moving object, but it is likely to be useful to observers only if the sampling preserves the impression of motion.

Changes in human infants' sensitivity to slow displacements over the first 6 months.

Sensitivity to slow movement improves substantially during the early postnatal months. Thresholds were measured for slow oscillatory displacements for 68 infants aged 6, 12, 18, and 24 weeks. Standing wave line stimuli were used; 6-week-olds were tested at 1.2 Hz, and infants in the three older age groups were tested at either 0.6 or 1.2 Hz. Six-week-olds as a group were very insensitive to these slow displacements. Sensitivity increased systematically across the three older ages. Thresholds were marginally lower at 1.2 Hz than at 0.6 Hz, and there was some indication that these thresholds may reflect a mixture of detection by position-sensitive and motion-sensitive mechanisms. Several factors are hypothesized to be responsible for this development: (1) improvements in spatial resolution; (2) improvements in temporal contrast sensitivity; (3) decreases in the size of second order motion integration mechanisms; and (4) increased neural connectivity in the motion pathways.

The selectivity of motion-driven visual attention in infants.

The onset of motion was used to study stimulus-driven visual attention in 14-week-olds. The movement of an object did not capture attention reflexively at 14 weeks of age. The attention-getting properties of a moving stimulus depended significantly on its color in combination with the colors of other objects in the visual field. Specifically, detection of a green moving target was masked in the presence of mixed red and green static objects. No such masking was observed when the moving target was red or when the green target moved in a visual field that was populated only with green objects. The same effect was observed to a lesser extent when the green bars were replaced with gray bars. The number of distractors in the visual field exerted an effect on the accuracy of detection only when their appearance in the visual field was coincident with the onset of target motion. Attention to motion at this age is not independent of the structure of the visual field; chromatic preferences play a role in how readily infants attend to a moving object. These effects may be mediated by a difficulty in disengaging attention (from distractors) or in suppressing attention to competing objects once attention is engaged on a target.

Motion-based detection by 14-week-old infants.

Three experiments using standing wave stimuli with 14-week-old human infants are reported. Two competing hypotheses regarding the detection of these standing wave line stimuli were tested in these studies. Amplitude-based (positional) detection was contrasted with speed-based (motion) detection. Temporal oscillation frequencies of 0.15, 0.30, 0.60 and 1.20 Hz were used. The detectability of a standing wave of fixed amplitude was influenced significantly by the temporal frequency of the oscillation. By inference, the results of the three experiments supported the motion-based detection hypothesis.

Role of image acceleration in judging landing location of free-falling projectiles.

The vertical acceleration of the projective image of a free-falling object specifies whether the object will land behind or in front of the observation site. Human sensitivity to this visual cue was investigated in 4 studies. Experiments 1 and 2 examined sensitivity to both constant and accelerating vertical acceleration. Detection of acceleration required a total change in velocity that was about 20% of the average velocity. In Experiments 3 and 4, subjects judged where computer-simulated free-falling objects would land relative to the observation site by viewing the initial segment of the flight objects whose trajectories remained in the sagittal plane of the observer. Judgments were influenced significantly by the magnitude and direction of the image velocity change even when no error feedback was available, implicating image acceleration as a source of information for judging the landing site of free-falling objects.

Rank orderings of photoreceptor photon catches from natural objects are nearly illuminant-invariant.

To examine the potential contribution of first-stage photoreceptor adaptation to color constancy, photon catches from 337 natural objects illuminated with phases of daylight and tungsten light were calculated for a model human fovea. The rank ordering of these photon catches within each cone photoreceptor class was examined. When first-stage adaptation is modeled using multiplicative or subtractive mechanisms, or a monotonic nonlinearity, no reordering of the rank ordering of photon catches is possible across illuminant changes. The observed rank orderings remained nearly invariant across illuminant changes for all three photoreceptor classes, although there was some local shifting in the rank orderings, thus ruling out the ability of von Kries adaptation alone to produce perfect color constancy. This means that for objects with natural reflectance spectra, the ordinal relationships between the photon catches within a class of photoreceptors exhibit only minor changes for these illuminant shifts. This result may be attributable to the fact that approx. 95% of the variance in these reflectance spectra is captured by the first principal component; objects that produce relatively few absorptions under one phase of daylight illumination will also produce relatively few absorptions under another phase. A geometric formalism for understanding these relationships is presented, and limitations on this analysis are discussed.

Two-dimensional approach to psychophysical orientation tuning.

Orientation bandwidths of psychophysical channels in the human visual system were inferred from contrast thresholds for a special class of polar-separable, two-dimensional patterns. Detection thresholds for these patterns conformed to a model with linear filtering by orientation-selective channels followed by probability summation across these channels. The number of channels (6-8 pairs) and their half-bandwidths at half-sensitivity (approximately 17 degrees) did not differ at 4 and 10 cycles/degree. The results extend the many one-dimensional, linear system models of vision to two dimensions.

The detection of slow stimulus movement in 2- to 5-month-olds.

Preferences for moving over static bars were assessed in 8-, 16-, and 20-week-old human infants. The display consisted of two adjacent horizontal bars one of which moved with one of four velocities (0.70, 1.4, 2.8 or 5.6 degrees/s) through one of four distances (11, 22, 44, or 88 arcmin) before reversing and traveling in the other direction at the same velocity. No significant preferences for motion were obtained at 8 weeks. At both 16 and 20 weeks of age, however, preferences for motion were determined exclusively by the velocity of the movement and were unaffected by the excursion of the bar. The minimum velocities that elicited significant preferences for motion were 5.08 degrees/s and 2.32 degrees/s at 16 and 20 weeks of age, respectively. The more attentive 20-week-olds, however, showed significant preferences for motion above a velocity of approximately 1.8 degrees/s. The addition of static reference bars had little influence on these preferences for motion in 20-week-olds; preferences were again related exclusively to the velocity of the bar's movement. The results are discussed in terms of the development of motion-sensitive mechanisms within the visual system.

Computational approaches to color constancy: adaptive and ontogenetic considerations.

Recent computational approaches to color constancy can be realized using a two-stage model of color vision. Adaptation at both the sensor stage and the second or reflectance channel stage is necessary to compute illuminant-invariant reflectance estimates. von Kries adaptation is shown to contribute significantly toward reducing, but not completely eliminating, the need for adaptation at the second stage. Examples of computations from the model using daylight illuminants, simulated natural reflectance functions, and putative human spectral sensitivity functions are shown. The ontogenetic plausibility of these models is also discussed. The role of the second-stage transformation in estimating surface reflectance is compared with the role of opponent color transformations in decorrelating primary receptor outputs.

A critical test of infant pattern preference models.

Models of infant visual preferences with predictions based on the physical attributes of visual patterns were evaluated using pairs of schematic faces and abstract patterns that were identical except for contrast reversals. Preferences at 6 weeks were entirely consistent with the predictions of these models. However, at 12 weeks the preferences for facelike images were in clear violation of the predictions of these models. These results represent the first unambiguous demonstration of a face preference in young human infants. The results also allow rejection of all current stimulus-based models of visual preference and suggest that a fundamental change in the determinants of visual preference occurs between 6 and 12 weeks postnatally.

Detection of stimulus motion in 5-month-old infants.

Five-month-old infants were tested by the method of preferential looking for discrimination between a pattern undergoing oscillating apparent motion and an identical static pattern. Sensitivity to small spatial displacements was evident at temporal frequencies of 8 and 16 Hz. Preference for the moving display was related independently to the temporal frequency of oscillation and the magnitude of the spatial displacement. Preferences for the moving display increased asymptotically across spatial displacements from 11 to 89 arc min. Preferences peaked between temporal oscillation frequencies of 8 and 16 Hz. Preference was not related to the ratio of these two variables--velocity. The minimum displacement threshold of 7.36 arc min was found to depend on the size of the elements in the pattern and on the temporal frequency of oscillation. The results demonstrate that motion-sensitive mechanisms responsive to small spatial displacements are present at 5 months of age.

A test of color constancy in 4-month-old human infants.

Forty-five 4-month-old infants were tested for color constancy using a familiarization, paired-comparison paradigm. Infants were familiarized and tested with colored stimuli under two conditions: (1) no change in the illuminant between familiarization and test and (2) a change in the illuminant between familiarization and test. Infants correctly recognized the familiarization color when tested with no change in the illuminant. Infants tested with a change in the illuminant correctly recognized the familiar color under some conditions yet failed to do so under others. Several explanations are considered for these results and it is concluded that color constancy operates immaturely at 4 months of age.