Causal cognition in a non-human primate: field playback experiments with Diana monkeys

Crested guinea fowls (Guttera pucherani) living in West African rainforests give alarm calls to leopards (Panthera pardus) and sometimes humans (Homo sapiens), two main predators of sympatric Diana monkeys (Cercopithecus diana). When hearing these guinea fowl alarm calls, Diana monkeys respond as if a leopard were present, suggesting that by default the monkeys associate guinea fowl alarm calls with the presence of a leopard. To assess the monkeys' level of causal understanding, I primed monkeys to the presence of either a leopard or a human, before exposing them to playbacks of guinea fowl alarm calls. There were significant differences in the way leopard-primed groups and human-primed groups responded to guinea fowl alarm calls, suggesting that the monkeys' response was not directly driven by the alarm calls themselves but by the calls' underlying cause, i.e. the predator most likely to have caused the calls. Results are discussed with respect to three possible cognitive mechanisms - associative learning, specialized learning programs, and causal reasoning - that could have led to causal knowledge in Diana monkeys.     

Improvement strategies in free-throw shooting and grip-strength tasks

Participants performed a free-throw shooting task and a grip-strength task before and after imagery, nonspecific arousal, or no instructions. Imagery improved performance in the free-throw shooting task, which is assumed to have more cognitive components than the grip-strength task. Imagery did not improve performance in the grip-strength task, which is assumed to have fewer cognitive components than the free-throw task. Nonspecific arousal, on the other hand, improved performance in the grip-strength task but not in the free-throw shooting task. Athletic experience, confidence levels, and gender were correlated with actual performance levels in both tasks, but not with improvement. Results are discussed within the transfer-appropriate processing framework.     

An object-based cost of visual filtering

Although evidence for object-based attention has been reported in a variety of paradigms, few studies have examined directly the relationship between efficiency in the processing of targets and the number of intervening distractors. In five experiments, observers judged whether the vertices of two relevant shapes were of the same height. Experiments 1 and 2 manipulated observers' perceptual set so that identical stimulus displays were perceived as containing either intervening or flanking distractors. The observers were faster when the distractors were flanking rather than intervening between the targets. Experiments 3-5 varied the number of intervening distractors directly. The observers' response latencies correlated positively with the distractor set-size. Because the distractors were highly discriminable from the targets and the spatial separation between the targets and their interactions with the adjacent distractors were held constant, it was unlikely that the differential reaction times across the conditions were caused by lateral inhibition or response competitions from the distractors. The results suggest the existence of an object-based filtering cost. The implications of the present data for attentional selection over noncontiguous regions are also discussed.     

Perceptual integration of motion and form information: evidence of parallel-continuous processing

In three visual search experiments, the processes involved in the efficient detection of motion-form conjunction targets were investigated. Experiment 1 was designed to estimate the relative contributions of stationary and moving nontargets to the search rate. Search rates were primarily determined by the number of moving nontargets; stationary nontargets sharing the target form also exerted a significant effect, but this was only about half as strong as that of moving nontargets; stationary nontargets not sharing the target form had little influence. In Experiments 2 and 3, the effects of display factors influencing the visual (form) quality of moving items (movement speed and item size) were examined. Increasing the speed of the moving items (> 1.5 degrees/sec) facilitated target detection when the task required segregation of the moving from the stationary items. When no segregation was necessary, increasing the movement speed impaired performance: With large display items, motion speed had little effect on target detection, but with small items, search efficiency declined when items moved faster than 1.5 degrees/sec. This pattern indicates that moving nontargets exert a strong effect on the search rate (Experiment 1) because of the loss of visual quality for moving items above a certain movement speed. A parallel-continuous processing account of motion-form conjunction search is proposed, which combines aspects of Guided Search (Wolfe, 1994) and attentional engagement theory (Duncan & Humphreys, 1989).     

Does P3 Reflect Attentional or Memory Performances,or Cognition more Generally?

The study evaluated the off-line relationship of attention, memory and other cognitive performances with the auditory event-related potentials P3 (P300) and N2. The sample comprised 200 middle-aged construction workers. Verbal, visuomotor and memory tests were administered. Attentional domains were examined using CogniSpeed software. Slowed reaction times in the test of sustained attention (vigilance) were associated with delayed P3 latency (p < 0.001) and decreased P3 amplitude (p = 0.005), as well as with delayed N2 latency (p < 0.001). Visuomotor slowing in Digit Symbol was also related to delayed P3 latency (p = 0.030) and decreased P3 amplitude (p = 0.014). In contrast, mild cognitive impairment, short- and long-term memory, and concentrating or sharing attention with high working memory demands were not related to P3. The results suggest that P3 is linked to attentional performance with low working memory demands rather than to effortful working memory updating, retrieval from memory stores, or mild cognitive impairment.     

Correspondence effects with manual gestures and postures: a study of imitation

In this study, the authors applied methods and theories from research of stimulus-response compatibility (SRC) to action imitation. In 6 experiments, they adopted the logic of the Simon paradigm (B. Hommel & W. Prinz, 1996) to explore interference between task-relevant symbolic stimulus features (color) and task-irrelevant iconic stimulus features (2 hand gestures and 2 postures). The same 2 hand gestures served as responses. Pronounced correspondence effects for both gestures and postures showed up throughout. In line with theories of SRC, the authors account for these correspondence effects in terms of overlap arising between stimulus and response features in a common representational domain. As a specific extension of this approach, they propose 2 functionally independent mechanisms: One operates movement-based when dynamic information is provided, and the other operates state-based with static postures as stimuli. Implications for theories of both SRC and action imitation are discussed.     

Perceiving binocular depth with reference to a common surface

A common surface is a spatial regularity of our terrestrial environment. For instance, we walk on the common ground surface, lay a variety of objects on the table top, and display our favorite paintings on the wall. It has been proposed that the visual system utilizes this regularity as a reference frame for coding objects' distances. Presumably, by treating the common surface as such--i.e. an anticipated constant--the visual system can reduce its coding redundancy, and divert its resources to representing other information. For intermediate-distance space perception, it has been found that absolute distance judgment is most accurate when a common ground surface is available. Here we explored if the common surface also serves as the reference frame for the processing of binocular-disparity information, which is a predominant cue for near-distance space perception. We capitalized on an established observation where the perceived slant of a surface with linear binocular-disparity gradient is underestimated. Clearly, if the visual system utilizes this incorrectly represented slant surface as a reference frame for coding the objects' locations, the perceived depth separation between the objects will be adversely affected. Our results confirm this, by showing that the depth judgment of objects (two laterally separated vertical lines) on, or in the vicinity of, the surface is underestimated. Furthermore, we show that the impact of the common surface on perceived depth separation most likely occurs at the surface-representation level where the visual surface has been explicitly delineated, rather than at the earlier disparity-processing level.     

Vertical and bisection bias in active touch

We investigated the conditions that underlie the vertical and bisection illusion in touch, in order to understand the basis of their similarity to visual illusions, and the means of reducing the biases in length perception by active touch. Movement, speed, and spatial reference cues were tested. Movements in scanning L-shapes in ipsilateral and contralateral (across the body midline) table-top space produced significant underestimation of the vertical line with the right hand, but not with the left hand. Right-handed scanning of L-shapes showed no significant bias when the vertical line in the figure was aligned to the body midline, suggesting that spatial cues were involved. The vertical line was overestimated in inverted T-shapes, but underestimated in rotated T-shapes, implicating line bisection. Holding scanning latencies constant reduced the vertical error for inverted T-shapes, but could not explain the bisection bias. Sectioning biases were predicted by the location of junctions on sectioned lines, showing that junction points act as misleading anchor cues for movement extents. The illusion was significantly reduced when reference information was added by instructing subjects to relate two-handed scanning of the figure to an external frame and to body-centred cues. It is argued that disparities in spatial reference (anchor) cues for movement extents are involved in vertical and bisection biases in active touch. The hypothesis that length illusions depend on disparities in spatial reference information can also account for the similarity of the tactile to the visual horizontal-vertical illusion.     

Thatcher illusion: dependence on angle of rotation

The expression of a face with its eyes and mouth inverted changes from 'pleasant' to 'grotesque' as the stimulus is rotated from 180 degrees to 0 degree (Thatcher illusion). We determined the angular orientation at which this change occurred for three manipulated faces. Mean thresholds for eighteen observers were found to lie between 94 degrees and 100 degrees relative to the vertical with an average overlap of about 15 degrees between an observer's ascending and descending thresholds. The sudden nature and relatively narrow zone of the changeover suggest a neuronal step-tuning of hypothetical face cells in the human brain, underlying the holistic ('grotesque') versus componential ('pleasant') processing of upright versus upside-down faces. Findings are discussed within the framework of cognitive, neuroimaging, and single-cell studies.