Dean G. Purcell

IT TAKES A CONFOUNDED FACE TO POP OUT OF A CROWD

It is widely reported that a picture of an angry face seems to figuratively pop out of an array of happy faces, although all of these reports are based on a single experiment by Hansen and Hansen. Pop out, when it occurs, indicates that an observer has located the target by means of a preattentive, parallel search. Hansen and Hansen concluded that it was the affect displayed by the face which caused it to pop out from its surrounding distracters. However, Hansen and Hansens angry faces contained extraneous dark areas which were introduced when they transformed Ekman and Friesens photographs of angry and happy faces into black-on-white sketches. When the original artifact-free gray-scaled versions of angry and happy faces were used no evidence for pop out was found. All target faces were found during a serial, self-terminating search regardless of their expression. The angry face in Hansen and Hansens experiments may have popped out from a crowd of happy faces because of a contrast artifact inadvertently introduced when they created their stimuli.

The face-detection effect: Configuration enhances detection

We have found that a picture of a face is more easily detected than is a pattern of arbitrarily rearranged facial features. An upright face is also more detectable than an inverted face. Using two-alternative forced-choice visual masking paradigms, we have found that this face-detection effect (FDE) can be produced with line drawings and with photocopies of a picture of a face. Our results suggest that a face, as an organized, meaningful pattern, is a more potent stimulus than an arbitrary assemblage of the same visual features. It may be that the FDE is a visual configuration effect. Previous visual configuration effects have been documented only with recognition responses. The FDE, by contrast, documents a configuration effect that affects the detectability of a stimulus.

Another look at semantic priming without awareness.

In a recent study, McCauley, Parmelee, Sperber, and Carr (1980) reported results indicating that semantic priming had been produced by visual stimuli that were backward masked at durations too brief for greater than chance report. The conclusions drawn from such an experiment are critically dependent upon whether or not the primes were actually masked below the thresh-old for identification during priming trials. The three experiments reported here provide evidence that this requirement was not met. Rather, McCauley et al.’s (1980) methodology allowed for an uncontrolled increase in light adaptation during the actual testing of prime efficacy in the priming session. This increase in light adaptation reduced the effectiveness of the backward mask and resulted in an increase in prime visibility during priming trials. Thus, semantic priming probably occurred under conditions in which commensurate visual information was actually available.

Visual angle and the word superiority effect.

Two experiments are reported in which a word superiority effect is obtained under conditions where a fixed set of alternatives are employed with positional certainty as to the critical letter, trial type (word or nonword) is mixed, and the subject is told to fixate the position of the critical letter. A third experiment employed the same methodology except for the fact that the stimuli subtended a larger retinal angle. No word superiority effect was observed in the third experiment. It is suggested that the visual angle of the stimulus display is a crucial factor in experiments on the word superiority effect.

Still another confounded face in the crowd.

Experiments using schematic faces developed by Öhman (Öhman, Lundqvist, & Esteves, 2001) seem to document an anger-superiority effect, although we have come to question these experiments. Our work shows that the low-level features of these schematic faces interact with the face’s surround to produce effects that have been attributed to facial affect. Using relatively neutral faces that preserved the feature and surround spatial relationships of angry and happy schematic faces, we produced reaction times (RTs) that were indistinguishable from those found with angry and happy faces. We also found that the target face’s position within the crowd determined the magnitude of the advantage for angry faces as well as for relatively affect-neutral faces. Removing the facial surround reduces the advantage for angry faces, largely by improving performance on happy faces. There was an apparent small advantage for angry features without a surround. öhman faces avoid the problems associated with modified grayscale faces only to introduce an equally troubling confound.

The object-detection effect: Configuration enhances perception

Line drawings used by Weisstein and Harris (1974) are seen as box-like three-dimensional figures if the lines are arranged properly. A flat two-dimensional pattern is seen when these same lines are disarranged. A target line contained within the three-dimensional figure is identified more readily than is the same line contained within a two-dimensional figure. This finding was extended in the present experiments: The three-dimensional stimulus was detected more quickly than the two-dimensional stimulus, under conditions of visual backward masking. Three-dimensional stimuli were also classified more quickly than two-dimensional stimuli. Just as with the face-detection effect and the word-detection effect, object detection can be affected by the form of the visual stimulus.

The word superiority effect: A comparison between restricted and unrestricted. alternative set

Three experiments were conducted to investigate the word superiority effect (WSE) (Reicher, 1969). The first two experiments used mixed presentations of words and nonwords, and positional uncertainty of the critical letter. Experiment 1 used an unrestricted set of alternatives, while Experiment 2 used only two alternatives (R and L). Experiment 3 compared letter detection in nonwords with a restricted and unrestricted alternative set. WSE was found for both Experiments 1 and 2, at about the same level. Experiment 3 showed superior performance when alternatives were known in advance. It was concluded that context has an effect on letter recognition even with prior knowledge of alternatives if the critical position is not known in advance. Some incompatibilities between the present results and those of other investigators in the field are discussed.

Some boundary conditions for a word superiority effect

A word superiority effect was obtained using a fixed stimulus set, positional certainty of the critical letter, mixed trial type, and instructions to fixate the critical letter. Control experiments established that this effect was not due to lateral masking. Further experiments extended the finding of a fixed-set word superiority effect to other stimulus sets, and to lowercase and mixed-case stimuli. The mixed-case word superiority effect is inconsistent with supraletter feature models of word recognition and, instead, lends support to hierarchical codes models. It was demonstrated that an unusually wide spacing of letters can disrupt the formation of word-level codes, and that wide visual angles are not necessarily disruptive as long as normal spacing is maintained.

Does Integration Produce Masking or Protect from it

To examine the role of integration in pattern masking, possible disruptive effects of integration were minimized by using a mask that overlaid completely all targets. Exposure durations were 10 ms, so under energy summation the target area was much darker than the rest. In another condition the mask was red and targets were blue, so under energy summation the target area could also be distinguished by hue. Masking magnitude increased with delay of mask onset, and it was established by four independent criteria that integration was negligible in the condition which produced most masking. It is deduced that integration is not necessary for masking; furthermore it is suggested that integration never produces masking, but rather may or may not protect from a disruptive effect of interruption. The argument is that were the visual system to have better visual resolution, it would suffer more given the same masking parameters. It is argued that type B masking functions arise from a combination of the facilitatory effect of integration and the detrimental effect of interruption.

Recovery and nonmonotone masking effects.

Recovery was produced by a homogeneous flash of light (M2). With M2 absent, correct letter report was a U-shaped curve when plotted against the interval separating the onset of a letter target and the onset of a patterned masking stimulus (M1). With the homogeneous flash of light ed to the stimulus sequence (target + M1 + M2), recovery occurred for all the shortest delays between the onsets of target and M1. Recovery peaked at a constant separation between the onsets of the target and M2, regardless, of the separation between the onsets of the target and M1. Current explanations of recovery cannot account for this result.