The Humean problem of induction and Carroll’s Paradox

Hume argued that inductive inferences do not have rational justification. My aim is to reject Hume’s argument. The discussion is partly motivated by an analogy with Carroll’s Paradox, which concerns deductive inferences. A first radically externalist reply to Hume (defended by Dauer and Van Cleve) is that justified inductive inferences do not require the subject to know that nature is uniform, though the uniformity of nature is a necessary condition for having the justification. But then the subject does not have reasons for believing what she believes. I defend a moderate externalist account that seeks to partly accommodate that objection to the radical externalist proposal. It is based on an extension of Peacocke’s theory of concepts: possession conditions for predicative concepts standing for natural properties include (fallible) dispositions to project them to new cases in accordance with inductive inferential patterns.

Choice and delay of reinforcement: Effects of terminal-link stimulus and response conditions

In two experiments, pigeons were exposed to concurrent-chains schedules in which a single initial-link variable-interval schedule led to access to terminal links composed of fixed-interval or fixed-delay schedules. In Experiment 1, an 8-s (or 16-s) delay to reinforcement was associated with the standard key, while reinforcer delay values associated with the experimental key were varied from 4 to 32 s. The results of Experiment 1 showed undermatching of response ratios to delay ratios with terminal-link fixed-delay schedules, whereas in some pigeons matching or overmatching was evident with the fixed-interval schedules. In Experiment 2, one pair of reinforcer delay values, either 8 versus 16 s or 16 versus 32 s, was used. In the first condition of Experiment 2, different delays were associated with different keylight stimuli (cued condition). In the second condition, different terminal-link delays were associated with the same stimulus, either a blackout (uncued-blackout condition) or a white key (uncued-white condition). To examine the role of responses emitted during delays, the keys were retracted during a delay (key-absent condition) in the third condition and responses were required by a fixed-interval schedule in the fourth condition. Experiment 2 demonstrated that the choice proportions for the shorter delay were more extreme in the cued condition than in the uncued-blackout condition, and that the response requirement imposed by the fixed-interval schedules did not affect choice of the shorter delay, nor did the key-absent and key-present conditions. These results indicate that the keylight-stimulus conditions affected preference for the shorter of two delays and that the findings obtained in Experiment 1 depended mainly on the keylight-stimulus conditions of the terminal links (i.e., the conditioned reinforcing value of the terminal-link stimuli).     

A quantitative analysis of sensitivity to the conditioned reinforcing value of terminal-link stimuli in a concurrent-chains schedule.

Pigeons were exposed to a concurrent-chains schedule in which a single variable-interval 30-s schedule was used in the initial links and fixed-time schedules were used in the terminal links. Three types of keylight conditions were used in the terminal links. In the first condition, different delays were associated with different keylight stimuli (cued condition). In the second condition, different delays were associated with the same stimulus, either a blackout (uncued blackout condition) or a white key (uncued white condition). Paired values of terminal-link fixed-time schedules differed by a constant ratio of 3:1, while the absolute value of delays was varied from 3 s to 54 s. The results showed that choice proportions for the shorter of two delays increased when the absolute size of the delays was increased for all keylight conditions. Further, the choice proportions for the shorter delay increased from the uncued blackout condition, to the uncued white condition, to the cued condition. A modified version of Fantino's (1969) delay-reduction model (expressed as a function relating the response ratio to the delay-reduction ratio) can be applied to these data by showing that sensitivity to delay reduction increased from the uncued blackout condition, to the uncued white condition, to the cued condition. Thus, the present study demonstrated that a modified version of the delay-reduction model can be used to assess quantitative differences in the terminal-link keylight condition in terms of sensitivity to delay reduction (i.e., the conditioned reinforcing value of the terminal-link keylight stimuli).     

Efficacy of constant time delay implemented by peer tutors in general education classrooms

We evaluated the effects of teaching 13 typically developing children to use constant time delay when tutoring three of their peers who had substantial disabilities. We measured the extent to which the tutors used the constant time delay procedure correctly and the tutees' correct performance on the skills being taught. A multiple probe design across behaviors was used. The results indicated that (a) the tutors used each step of the constant time delay with a high degree of procedural fidelity; (b) the students with disabilities acquired the skills that were taught during peer tutoring; and (c) modifications of the procedure were required for 2 of the 3 students with disabilities, and the peers tutors were able to implement the modifications. Implications for practice and future research are described.     

Differential Effects of Two Spelling Procedures on Acquisition,Maintenance and Adaption to Reading

An alternating treatments design was used to assess the effects of a constant time delay (CTD) procedure and a cover-copy-compare (CCC) procedure on three students’ acquisition, subsequent maintenance, and adaptation (i.e., application) of acquired spelling words to reading passages. Students were randomly presented two trials of word lists from their respective curriculum under each condition once daily. Results suggest that both procedures were effective for helping students efficiently acquire spelling words, but the CCC condition resulted in more words learned for all participants, although less pronounced when instructional time was considered. However, the CTD procedure resulted in substantially higher levels of maintenance for Jeremy and Leon, with no significant difference between the two procedures for the Anthony. Adaptation of acquired spelling words to reading was about equal under both conditions for Anthony and Leon, while Jeremy showed higher levels of performance in the CTD procedure. Discussion focuses on discrepant results, matching instructional procedures to specific learning concerns, and directions for future research.     

Delayed signal detection, differential reinforcement, and short-term memory in the pigeon.

In two discrete-trial delayed-detection experiments, six pigeons were trained on dependent concurrent variable-interval schedules. Pecking a red side key was reinforced when the brighter of two white lights (S1) had been presented on the center key, and pecking a green side key was reinforced when the duller of two white lights (S2) had been presented on the center key. Incorrect responses were red side-key pecks following S2 presentations and green side-key pecks following S1 presentations; these resulted in three-second blackouts. In Experiment 1, the time between presentation of S1 or S2 on the center key and the onset of the red and green side keys was varied nonsystematically from 0.06 seconds to 19.69 seconds across experimental conditions. Stimulus discriminability decreased as the stimulus-choice delay increased. A rectangular-hyperbolic function better described this decrease in discriminability over time than did a negative-exponential function. In Experiment 2, at each of three stimulus-choice delays (0.06, 3.85, and 10.36 seconds), relative reinforcer frequency for correct responses to the red and green side keys was varied by changing the values of the dependent concurrent variable-interval schedules. The sensitivity of choice to relative reinforcer frequency was independent of the decrease in stimulus discriminability with increasing stimulus-choice delay.     

The use of the mental development index of the Bayley scale to diagnose language delay in 2-year-old high-risk infants

To determine if a detailed analysis of the language items of the Bayley Scales of Infant Development (BSID) would be useful in detecting language delay, the Bayley Mental Development Index (MDI) and Reynell Developmental Language Scales (RDLS-R) were administered to 137 low-birthweight infants at 2 years of age. In spite of scores in the normal range on the BSID, many of these children had significantly delayed language. However, the children with delayed language could be detected on the basis of detailed analysis of certain language items of the MDI, indicating that these items are more useful than the total MDI score.     

Subliminal speech perception and auditory streaming

Current theories of consciousness assume a qualitative dissociation between conscious and unconscious processing: while subliminal stimuli only elicit a transient activity, supraliminal stimuli have long-lasting influences. Nevertheless, the existence of this qualitative distinction remains controversial, as past studies confounded awareness and stimulus strength (energy, duration). Here, we used a masked speech priming method in conjunction with a submillisecond interaural delay manipulation to contrast subliminal and supraliminal processing at constant prime, mask and target strength. This delay induced a perceptual streaming effect, with the prime popping out in the supraliminal condition. By manipulating the prime-target interval (ISI), we show a qualitatively distinct profile of priming longevity as a function of prime awareness. While subliminal priming disappeared after half a second, supraliminal priming was independent of ISI. This shows that the distinction between conscious and unconscious processing depends on high-level perceptual streaming factors rather than low-level features (energy, duration).     

Short-term remembering of discriminative stimuli in pigeons.

Pigeons learned to peck the left or right of two white keys depending on whether a red or a green stimulus was displayed on a third key. The opportunity to peck the white keys was then dealyed for zero to six seconds after the red or green (to-be-remembered) stimulus. On half the trials, the feeder operated during the delay to interrupt behavior that might mediate discriminated responding. No events were scheduled on the remaining trials. In a later condition, the pigeons had the opportunity to peck the white keys during the delay. In general, accuracy decreased as delay increased in all conditions, but performance was least accurate following feeder operations and most accurate when pecking was allowed during the delay. The procedures may be analogous to varying the opportunity for rehearsal in studies of human short-term memory.