How do predators generalize warning signals in simple and complex prey communities? Insights from a videogame

The persistence of distinct warning signals within and between sympatric mimetic communities is a puzzling evolutionary question because selection favours convergence of colour patterns among toxic species. Such convergence is partly shaped by predators' reaction to similar but not identical stimulus (i.e. generalization behaviour), and generalization by predators is likely to be shaped by the diversity of local prey. However, studying generalization behaviour is generally limited to simple variations of prey colour patterns. Here, we used a computer game played by humans as surrogate predators to investigate generalization behaviours in simple (4 morphs) and complex (10 morphs) communities of unprofitable (associated with a penalty) and profitable butterflies. Colour patterns used in the game are observed in the natural populations of unprofitable butterfly species such as Heliconius numata . Analyses of 449 game participants' behaviours show that players avoided unprofitable prey more readily in simple than in complex communities. However, generalization was observed only in players that faced complex communities, enhancing the protection of profitable prey that looked similar to at least one unprofitable morph. Additionally, similarity among unprofitable prey also reduced attack rates only in complex communities. These results are consistent with previous studies using avian predators but artificial colour patterns and suggest that mimicry is more likely to evolve in complex communities where increases in similarity are more likely to be advantageous.

Paradoxical differences in pain ratings of the same stimulus intensity

Aims Stimulus intensity used for assessing temporal summation of pain (TSP) is commonly set at the participants’ pain tolerance. Yet pain ratings during TSP rarely reach that initial pain tolerance pain rating. This study aimed to explore the differences between baseline pain tolerance assessed by cuff algometry and subsequent pain ratings of the same stimulus intensity, and the reliability of these ratings over 2 sessions. Methods In two sessions, separated by one week, 24 healthy, pain-free males had their pressure pain detection (PDT) and tolerance threshold (PTT) recorded using a staircase inflation paradigm (5 kPa increments, 1sec-ON:4sec-OFF) with a cuff algometry system. The pain intensity was assessed during cuff stimulation using an electronic visual analogue scale (VAS, 0–10 cm). Three different inflation paradigms were then performed, using the PTT level as stimulation intensity, and a 1-s duration for each stimulus: PEAKS: 3 inflations at 0.17 Hz, SLOW: 10 inflations at 0.01 Hz, FAST: 10 inflations at 0.5 Hz). Approximately 5-min was kept between the staircase assessment and the first stimulation paradigm, and between each of the 3 inflation paradigms. The PTT and first inflation VAS rating from each paradigm was extracted. Results The VAS rating of PTT pressure was higher in the staircase (VAS: 8.5±2.1 cm) than the first PPT stimulus in any other paradigm (PEAKS: 5.4±2.0; SLOW: 4.6±2.1; FAST: 4.0±2.3, P < 0.05). VAS ratings were also lower in each subsequent paradigm (i.e. PEAKS > SLOW > FAST, P < 0.05). Intra-class coefficients demonstrated excellent reliability for each paradigm (all ICC > 0.79) between sessions. Conclusions PTT, as assessed with the staircase inflation paradigm, was rated more painful during baseline assessment than when the identical stimulus profile (PPT intensity for 1-s) was applied afterwards and this finding is considered reliable.

Dissociative Experiences and Reality-Testing Deficits in College Students

One hundred forty-one college students completed a computerized test of reality-monitoring deficits and a computerized version of the Dissociative Experiences Scale (DES). In the test of reality-monitoring, subjects fixated on a dot, perceived a stimulus to one side, imaged an identical stimulus on the other side and rated its vividness while continuing to image. Then, either the dot became a P and subjects pressed a button on the side of the percept, as quickly as possible, or the dot became an I and subjects pressed a button on the side of the image. Subjects exhibiting above-median scores on the Dissociation/Amnesia factor of the DES took longer to discriminate perception from vivid imagery than from faint imagery, as if they failed to monitor the greater “central innervation” behind more vivid, more percept-like imagery. These results corroborate recent findings that dissociative tendencies in college students, like psychotic tendencies in students, have reality-testing deficiencies at their core.

Cognitive Variability: The Ubiquity of Multiplicity

No one doubts that immense variability exists at the neural level. Even when the identical stimulus is presented repeatedly within a single experimental session, the response of an individual neuron varies from trial to trial. Similarly, with lowlevel cognitive processes such as association, there is no disagreement concerning the existence of competing units. Models of associative memory, both symbolic (e.g., Gillilund & Shiffrin, 1984) and subsymbolic (e.g., Seidenberg & McClelland, 1990), are predicated on the assumptions that stimuli have multiple associations and that these varying associations influence the way in which we remember. Higher level cognition, however, has been treated differently. Many models are universalist: Everyone is depicted as proceeding in the same way when relevant stimuli are presented. Other models are comparative; they hypothesize different ways of thinking among groups defined on the basis of such characteristics as age, expertise, or aptitudes, but hypothesize a single consistent kind of reasoning within each group. Thus, 8-year-olds might be depicted as performing in one way and 5-year-olds in another, experts in one way and novices in another, people with high spatial ability in one way and those with low spatial ability in another, and so on. The finest differentiations that are typically made within these comparative approaches examine individual differences within people of a single age; for example, reflective 8-year-olds are described as taking a long time but answering accurately on the Matching Familar Figures Test, and impulsive 8-year-olds are described as answering more quickly but less accurately (Kogan, 1983). The main purpose of this chapter is to summarize the rapidly growing body of research suggesting that variability is actually a pervasive reality in high-level, as well as low-level, cognition. To place this work in context, however, it seems useful first to briefly consider some prominent examples of universalist and comparative models of cognition and then to consider why they might be proposed and widely accepted even if thinking is far more variable than they depict it as being. A great deal of cognitive research has been devoted to identifying the processing approach that people use on a particular task. This universalist approach has led to many influential models and theories.

Personality Traits and Reality-Testing Abilities, Controlling for Vividness of Imagery

One hundred seventy-seven college students completed personality measures including the MMPI-168, and reality-discrimination measures including a timed discrimination task developed by the first author. Previously on such a timed task, normal subjects discriminated percepts more quickly from images of perceptual vividness than from faint images, as if they registered more “central innervation” during more vivid imaging. Presently, on each of the four practice trials and forty-four timed trials in Task 1, subjects fixated on a dot, perceived a stimulus to one side, imaged an identical stimulus on the other side and rated its vividness while continuing to image. Then, either the dot became a P and subjects pressed a button on the side of the percept, as quickly as possible, or the dot became an I and subjects pressed a button on the side of the image. The slope, within subject, of image/percept discrimination times over image-vividness ratings was computed for the 149 subjects who rated some of their forty-four images more vividly than others. It was predicted and found that self-described hallucinators and MMPI-defined paranoids discriminated percepts less quickly from vivid images, as if the greater “central innervation” behind more vivid images is not registered by psychosis-prone subjects.

The Nature of Preattentive Storage in the Auditory System

Event-related potentials were recorded to tones that subjects ignored while reading a book of their choosing. In all conditions, 90% of the tones were 100 msec in duration and 10% of the tones were 170 msec in duration. In a control condition, a customary oddball paradigm was used in which all of the tones were identical except for the longer duration tones. In two conditions, the tones varied over a wide range of tonal frequencies from 700 to 2050 Hz in 10 steps of 150 Hz. In another condition, the tones varied over the same frequencies but also varied in intensity from about 60 to 87 dB in steps of 3 dB. Thus, there was no “standard” tone in the sense of a frequently presented tone that had identical stimulus features. A mismatch negativity (MMN) was elicited in all conditions. The data are discussed in terms of the storage of information in the memory upon which the MMN is based.

Ventilatory pattern after hypoxic stimulation during wakefulness and NREM sleep

The ventilatory after-discharge mechanism (VAD) may stabilize ventilation (VE) after hyperventilation but has not been studied in detail in humans. Several studies conducted during wakefulness suggest that VAD is present, although none has been conducted during sleep, when disordered ventilation is most common. We conducted two experiments during wakefulness and non-rapid-eye-movement (NREM) sleep in 14 healthy young men to characterize the ventilatory response after termination of a 45- to 60-s 10–12% O2 hypoxic stimulus. Eight subjects had triplicate hypoxic trials terminated by 100% O2 during wakefulness and NREM sleep. Hypoxia caused a drop in arterial O2 saturation to 78.5 +/- 0.5%, an increase in VE of 4.4 +/- 0.6 l/min, and a decrease in end-tidal PCO2 of 4.4 +/- 0.4 Torr during wakefulness, with no significant differences during sleep. When the hypoxia was terminated with 100% O2, VE was variable within and between subjects during wakefulness. During sleep, all subjects developed hypopnea (VE < 67% baseline) with a mean decrease of 65.5 +/- 7.8% at the onset of hyperoxia (P < 0.05 compared with baseline VE). We hypothesized that this uniform decrease in VE might be due to the nonphysiological hyperoxia employed. We therefore studied six additional subjects, all during NREM sleep, with identical hypoxic stimulation of breathing terminated by 100% O2 or room air. We again found that termination of hypoxia with 100% O2 produced uniform hypoventilation. However, when the identical stimulus was terminated with room air, no hypoventilation occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Primate premotor cortex: dissociation of visuomotor from sensory signals

1. If we assume adequate control for attention, memory, and stimulus location, a bona fide sensory response would be unaffected by whether a visuospatial stimulus instructs (1) one limb movement versus another or (2) limb movement versus a shift in spatial attention or memory. Two behavioral methods tested whether apparently sensory responses in the monkey's premotor cortex are strictly that, or, alternatively, whether they reflect the action instructed by a stimulus. 2. When an identical stimulus leads to two different responses, phasic discharge after a visuospatial stimulus is significantly, often dramatically, affected by the response. Similarly, premotor cortex neurons discharge more after a stimulus instructs a limb movement than after the same stimulus instructs a shift in spatial attention or memory. Thus, for the majority of premotor cortex neurons, the hypothesis that phasic poststimulus activity modulation represents a sensory response can be rejected.

Atrial inotropic responses to brief vagal stimuli: frequency-force interactions

The effect of brief vagal stimulus burst on atrial contractile force was assessed in paced- and unpaced-heart preparations by recording the changes in pressure (AP) generated in a balloon in the right atrial appendage or by a miniature strain gauge on the atrium. One and 3 stimuli per vagal burst depressed AP up to 62 and 90%, respectively. The response varied with the time in the cardiac cycle at which the stimulus was given. Identical stimuli produced a greater inotropic depression at longer cardiac cycle durations. The differences between the magnitudes of the AP responses at two different mean heart rates were relatively constant when the stimulus intensity was increased from 1 to 99 stimuli per burst. A low-level stimulus caused a greater depression in contractile force when the heart rate was allowed to change than with the identical stimulus when the heart was paced, although this difference in paced- and unpaced-heart responses tended to disappear when the stimulus intensity (burst width) was increased. The composite frequency-force relationship was relatively flat over normal heart periods, but fell off by 15-20% at the extremes. The present results show an unexpected interaction between the vagal inotropic effect and the frequency-force relationship such that a given vagal stimulus causes a greater depression of atrial contractile force at lower heart rates.