Martin L. Richter

The generality of learned helplessness in the rat

Abstract Two experiments were simultaneously conducted in which two different groups of 40 rats each were exposed to one of two different stressors. In both experiments half the subjects were pretreated with shock, half with underwater exposure. For each pretreatment stressor, half the subjects were allowed to escape, the other half were not. The experiments differed in the test task used. Approximately 24 hr after pretreatment, one-half the subjects from each pretreatment group received 20 water-escape trials in an underwater maze, the other half received 20 shock-escape trials in a two-way shuttle box. The subjects in each of the inescapable pretreatment conditions were slower to escape in the subsequent shock-escape and water-escape tasks when compared with subjects in the corresponding escapable pretreatment condition. The “learned helplessness” effect appeared to be no smaller when aversive stimuli were changed between pretreatment and test than when they remained the same.

Pronounceability and the Visual Recognition of Nonsense Words.

Additional evidence is presented for the hypothesis that visual word recognition may involve recording into phonemic form. Specifically, the hypothesis that less pronounceable nonsense words are recognized as nonsense faster than more pronounceable nonsense words was confirmed. It is proposed that differences in pronounceability produce their effects during the sequencing of the neural instructions associated with each phoneme.

The Category-Confound: A Design Error

Summary An experimental design problem, found to be frequent in some of the social psychology literature, occurs when only one sample from a population of possible samples is used to define a category of treatment factors. An example would be using one man and one woman as Es to test the effect of sex of E. This error, called the category-confound, leads to an inability to generalize treatment effects beyond the particular sample chosen, and to an inability to perform the appropriate significance tests. Several examples are discussed in detail, and the frequency of occurrence of this error in two recent journals in social psychology are surveyed. In most cases the category-confound can be dispelled simply by taking an adequately large sample from the population.

The roles of expectancy and aftereffects in alternation

Abstract In each of three experiments rats were pretreated in straight alleys to discriminate the brightness of an alley as signal for the magnitude of reward. Then the rats were tested in E-shaped mazes in which reward varied across trials and in which the brightness of the stem signaled the magnitude of reward. In all three experiments the rats alternated more on trials following a small reward on the previous trial, and in the third experiment the rats alternated more on those trials where a small reward was signaled. Rats choice responses on Trial n were also affected by the stimulus/reward and choice on Trial n − 2 and by the relationship between stimuli/rewards on Trials n − 2 and n . These results were interpreted as a tendency by the rat to change a less satisfactory situation by varying its response, and to retain a more satisfactory situation by perseverating in its choice response.

Attack intensity by two species of territorial damselfish (Pomacentridae) as estimates of competitive overlap with two species of wrasse (Labridae)

The intensity of interspecific territorial defense should be based upon the degree of competitive overlap. We tested this relationship in two territorial Caribbean damselfish (dusky, Stegastes adustus, and longfin, S. diencaeous) with intruders being the bluehead wrasse (Thalassoma bifascatus) and the slippery dick wrasse (Halichoeres bivittatus). Based on food habits, the slippery dick and the bluehead wrasse should have the same degree of competitive overlap to the two damselfish species. We also predicted that the larger slippery dick wrasse intruder would receive more aggression than the smaller bluehead wrasse intruder. Neither damselfish species distinguished between the two wrasses suggesting that they were ecologically equivalent. We also tested size differences within both species of wrasse and found that size had no influence on the aggression in the dusky damselfish. The longfin also did not show a size preference for the bluehead but did prefer to attack the larger slippery dick wrasse. In spite of the similarities between the dusky and the longfin damselfish and the similar food habits of the bluehead and the slippery dick wrasse, our results suggest that using intensity of interspecific territorial defense alone may not be an adequate measure of competitive overlap.

Are conspecific and heterospecific opponents assessed similarly? A test in two species of territorial damselfish (Pomacentridae)

Aggression is often a crucial component to interference interspecific competition and yet there are few studies that examine fight behavior when the opponents are different species. To examine conspecific and heterospecific aggression, we used two species of Caribbean damselfish, the dusky (Stegastes adustus) and the longfin (S. diencaeous) with each one serving as the heterospecific opponent to the other species. Our study was confined to whether or not each species measures the body length of the other species as if it were a conspecific intruder. Body length plays an important role in fight outcome in many species of fish and we presumed that both the dusky and the longfin would use it when assessing opponents. Both the dusky and the longfin damselfish were then presented with two individuals that were either greatly different or minimally different in size. When presented with individuals that differed greatly in size, both species spent more time attacking the larger individual, irrespective of species. However, when the size difference was small, the focal dusky and the longfin responded differently; the dusky showed no preference in either conspecific or heterospecific pairs while the longfin continued to show a bias toward the slightly larger individual. Thus, while we were surprised by the species differences, both the dusky and the longfin were internally consistent in how they treated conspecific and heterospecific opponents.

Territorial vocalization in sympatric damselfish: acoustic characteristics and intruder discrimination

Abstract Damselfishes are well known for their aggressive, territorial behaviour during which the use of vocalization behaviour has been well documented. However, agonistic acoustic signalling has been understudied in particular when the vocalizations are interspecific. In this study, we characterize and compare the previously undescribed vocalization behaviour of longfin damselfish (Stegastes diencaeus), in an agonistic context, with the closely related and sympatric dusky damselfish (Stegastes adustus). Next, we examined if these congeneric species modulate their vocalizations in a similar pattern to previously described aggressive behaviour patterns. Audio field recordings of territorial males were obtained in response to three separate stimuli: (1) conspecific male damselfish, (2) heterospecific male damselfish and (3) a common intruder, the slippery dick wrasse (Halichoeres bivittatus). The vocal repertoires of both longfin and dusky damselfish comprised the same three distinct call types: chirps, pops and pulse trains. However, temporal measures of the calls showed significant differences between species. Additionally, dusky damselfish were more vocal overall, producing more calls and spending more time calling than longfin damselfish. These responses were stimulus and species dependent, as the two species modulated acoustic response by modulating pulse number based on intruder species. These results suggest that these closely related species of damselfish use vocalization behaviours that are both unique and context dependent.