When do ratings implicate perception versus judgment? The “overgeneralization test” for top-down effects

ABSTRACT

When looking at an object—say, a banana—we can both directly perceive its visual qualities (e.g., its size) and also make higher-level judgments about its visual and non-visual properties (e.g., not only its size, but also its cost). Suppose you obtain a rating of a property such as size. Does that rating implicate seeing or merely higher-level judgment? The answer often matters a great deal -- e.g., determining whether such ratings imply “top-down” effects of cognition on perception. Too often, however, this distinction is ignored in empirical investigations of such effects. Here we suggest a simple test for when such ratings can be used to implicate perception: whenever the very same experiment “overgeneralizes” to an unambiguously non-perceptual factor, the results cannot be used to draw implications about perception, per se. As a case study, we investigate an empirical report alleging that conservatives perceive Barack Obama as darker skinned than liberals do. Two simple experiments show that the very same effects, measured via the same “representativeness” ratings, obtain with unambiguously non-perceptual and even silly factors (involving bright red horns vs. halos, rather than brightness differences). We suggest that this renders such methods unable to implicate visual processing and we recommend that “overgeneralization tests” of this type always be conducted in such contexts.     

Human and machine perception of biological motion

More than 30 years ago, Johansson was the first to show that humans are capable of recovering information about the identity and activity of animate creatures rapidly and reliably from very sparse visual inputs – the phenomenon of biological motion. He filmed human actors in a dark setting with just a few strategic points on the body marked by lights – so-called moving light displays (MLDs). Subjects viewing the MLDs reported a vivid impression of moving human forms, and were even able to tell the activity in which the perceived humans were engaged. Subsequently, the phenomenon has been widely studied and many attempts have been made to model and to understand it. Typical questions that arise are: How precisely is the sparse low-level information integrated over space and time to produce the global percept, and how important is world knowledge (e.g., about animal form, locomotion, gravity, etc.)? In an attempt to answer such questions, we have implemented a machine-perception model of biological motion. If the computational model can replicate human data then it might offer clues as to how humans achieve the task. In particular, if it can do so with no or minimal world knowledge then this knowledge cannot be essential to the perception of biological motion. To provide human data for training and against which to assess the model, an extensive psychophysical experiment was undertaken in which 93 subjects were shown 12 categories of MLDs (e.g., normal, walking backwards, inverted, random dots, etc.) and were asked to indicate the presence or absence of natural human motion. Machine perception models were then trained on normal sequences as positive data and random sequences as negative data. Two models were used: a k-nearest neighbour (k-NN) classifier as an exemplar of ‘lazy’ learning and a back-propagation neural network as an exemplar of ‘eager’ learning. We find that the k-NN classifier is better able to model the human data but it still fails to represent aspects of knowledge about body shape (especially how relative joint positions change under rotation) that appear to be important to human judgements.     

Multistable perception: when bottom-up and top-down coincide

During prolonged observation of an ambiguous figure sudden perceptual reversals occur, while the stimulus itself stays unchanged. There is a vivid debate about whether bottom-up or top-down mechanisms underlie this phenomenon. In the present study, we investigated the interrelation of two experimental factors: volitional control and discontinuous stimulus presentation. Both factors strongly modulate the rate of perceptual reversals and each is attributed either as top-down or bottom-up. We found that participants can apply specific strategies to volitionally increase and/or decrease the stability duration of each of the possible percepts according to the experimental instructions. When attempts of volitional control are combined with discontinuous stimulus presentation the effects are fully additive. Our results indicate that perceptual reversals can originate from different neural mechanisms on different time scales.     

The conceptual grouping effect: categories matter (and named categories matter more)

Do conceptual categories affect basic visual processing? A conceptual grouping effect for familiar stimuli is reported using a visual search paradigm. Search through conceptually-homogeneous non-targets was faster and more efficient than search through conceptually-heterogeneous non-targets. This effect cannot be attributed to perceptual factors and is not explained by a long-term representational reorganization due to perceptual-learning. Rather, conceptual categories seem to modulate visual representations dynamically, and are sensitive to task-demands. Verbally labeling a visual target further exaggerates the degree to which conceptual categories penetrate visual processing.     

Attention and the Cognitive Penetrability of Perception

One sceptical rejoinder to those who claim that sensory perception is cognitively penetrable is to appeal to the involvement of spatial attention. While the sceptic is correct that some putative cases are accurately deflected in this way, the rejoinder oversimplifies the possible roles that attention might play in relevant contexts. This paper identifies alternative ways that selective attention might play a role in cognitive effects on perception. What emerges is a plausible and well-evidenced mental schema that describes attention-mediated cognitive penetration.     

Self-directed speech affects visual search performance

People often talk to themselves, yet very little is known about the functions of this self-directed speech. We explore effects of self-directed speech on visual processing by using a visual search task. According to the label feedback hypothesis (Lupyan, 2007a), verbal labels can change ongoing perceptual processing—for example, actually hearing “chair” compared to simply thinking about a chair can temporarily make the visual system a better “chair detector”. Participants searched for common objects, while being sometimes asked to speak the target's name aloud. Speaking facilitated search, particularly when there was a strong association between the name and the visual target. As the discrepancy between the name and the target increased, speaking began to impair performance. Together, these results speak to the power of words to modulate ongoing visual processing.     

Similar effects of visual perception and imagery on simple reaction time

A longstanding issue is whether perception and mental imagery share similar cognitive and neural mechanisms. To cast further light on this problem, we compared the effects of real and mentally generated visual stimuli on simple reaction time (RT). In five experiments, we tested the effects of difference in luminance, contrast, spatial frequency, motion, and orientation. With the intriguing exception of spatial frequency, in all other tasks perception and imagery showed qualitatively similar effects. An increase in luminance, contrast, and visual motion yielded a decrease in RT for both visually presented and imagined stimuli. In contrast, gratings of low spatial frequency were responded to more quickly than those of higher spatial frequency only for visually presented stimuli. Thus, the present study shows that basic dependent variables exert similar effects on visual RT either when retinally presented or when imagined. Of course, this evidence does not necessarily imply analogous mechanisms for perception and imagery, and a note of caution in such respect is suggested by the large difference in RT between the two operations. However, the present results undoubtedly provide support for some overlap between the structural representation of perception and imagery.     

Visually guided capture of a moving stimulus by the pigeon (Columba livia)

Although the pigeon is a popular model for studying visual perception, relatively little is known about its perception of motion. Three experiments examined the pigeons’ ability to capture a moving stimulus. In Experiment 1, the effect of manipulating stimulus speed and the length of the stimulus was examined using a simple rightward linear motion. This revealed a clear effect of length on capture and speed on errors. Errors were mostly anticipatory and there appeared to be two processes contributing to response locations: anticipatory peck bias and lag time. Using the same birds as Experiment 1, Experiment 2 assessed transfer of tracking and capture to novel linear motions. The birds were able to capture other motion directions, but they displayed a strong rightward peck bias, indicating that they had learned to peck to the right of the stimulus in Experiment 1. Experiment 3 used the same task as Experiment 2 but with naïve birds. These birds did not show the rightward bias in pecking and instead pecked more evenly around the stimulus. The combined results indicate that the pigeon can engage in anticipatory tracking and capture of a moving stimulus, and that motion properties and training experience influence capture.     

Effects of nicotine administration via a sublingual tablet on arousal and verbal ability in non‐smokers

Tobacco smoking or nicotine administration on its own can influence cognitive task performance. This study examined the effects of acute nicotine administration on verbal task performance and a physiological index of arousal. Healthy non‐smoking participants received either a 2‐mg sublingual nicotine tablet or placebo. Participants next completed various verbal tasks while heart rate recordings were taken concurrently. Nicotine increased heart rate relative to a pre‐administration baseline period, indicating that the new method of nicotine administration increased cardiovascular arousal. Nicotine was associated with reduced accuracy in a verbal matching task and reduced accuracy and increased reaction time in an anagram task, but had no effect on performance during an analogy or verbal fluency task. The data suggest that nicotine‐naïve individuals are unlikely to gain any benefit to their verbal ability from the single acute intake of nicotine, such as that obtained from cigarette smoking or by using nicotine replacement therapy products.     

Setting the stage subliminally: unconscious context effects

An important approach to understand how the brain gives rise to consciousness is to probe the depth of unconscious processing, thus to define the key features that cause conscious awareness. Here, we investigate the possibility for subliminal stimuli to shape the context for unconscious processing. Context effects have generally been assumed to require consciousness. In the present experiment, unconscious context processing was investigated by looking at the impact of the context on the response activation elicited by a subliminal prime. We compared the effects of the same subliminal prime on target processing when the prime was embedded in different unconscious contexts. Results showed that the same prime can evoke opposite responses depending on the unconscious context in which it is presented. Taken together, the results of this study show that context effects can be unconscious.     

Attributions for Memory Performance in Adulthood: Age Differences and Mediation Effects

We examined age differences in attributions to internal (controllable and uncontrollable), external (uncontrollable), and unstable factors for performance on a free recall memory task in 149 young, middle-aged, and older adults. Attributions varied by age and by level of memory performance. Middle-aged and older adults rated internal, uncontrollable factors (ability and genes) as more influential for high performance than for low performance, and they were less likely than young adults to attribute low performance to these factors. Within age groups, only the older adults rated memory ability as more influential than strategy use, even though they were as likely as the other age groups to use a categorization strategy. Attributions to both internal controllable (strategy use) and uncontrollable (ability) factors as well as to health were associated with better memory performance. These attributions partially mediated the relationship between age and memory performance. Thus, attributions may provide some insight into sources of age differences in memory performance.     

西方四种心理学流派近19年在中国的发展

本文通过对 1 980～ 1 998年间 6种“核心”心理学期刊所发表论文题目的关键词、参考文献引用杂志的分析 ,对认知心理学、行为主义、精神分析和神经科学四种心理学流派在中国的发展做了研究 ,得出以下结果 :(1 )认知心理学研究论文的数量快速增长 ,神经科学领域的研究略有增加 ;(2 )四学派在中国受重视的程度依次为认知心理学、神经科学研究、行为主义、精神分析 ;(3 )精神分析和行为主义的研究极少。