Absolute identification with simple and complex stimuli

It is well known that people can perfectly identify only a handful of distinct unidimensional stimuli, such as line lengths, but can identify thousands of complex stimuli, such as letters and words. This result is consistent with capacity limits in identifying unidimensional stimuli but not complex stimuli. The experiments reported here tested this theoretical dissociation using Luce's (1963) Similarity Choice Model to measure the psychological distance between stimuli in line-length-identification and letter-identification tasks. The psychological distance between line-length stimuli decreased with the number of to-be-identified stimuli; this result is concordant with capacity limits in unidimensional absolute identification. Surprisingly, the opposite result held in letter identification. Psychological distance between letters increased with an increased number of to-be-identified stimuli. This result indicates an opposite type of processing deficit: People process letters more efficiently with more choices.     

RT to tactile stimuli presented ipsi- and contralaterally to the responding hand

Subjects had to react with the hand which received a tactile stimulus (uncrossed condition) or with the hand opposite to the hand which received the stimulus (crossed condition). Four experiments were conducted. In the first three, subjects knew which hand would receive the stimulus and which hand would have to respond. In the first two experiments, subjects reacted to a simple tactile stimulus while in the third subjects had to perform a tactile discrimination before responding. No significant differences in RT under the crossed and uncrossed conditions were observed in the first three experiments. In the fourth experiment, subjects did not know which hand would receive the stimulus, and they also did not know which hand would have to respond. Under these conditions, large significant differences in RT between the crossed and uncrossed condition emerged.

The study includes a criticism of a simple structural interpretation of interhemispheric transmission time (IHTT) as proposed by Bashore (1981). Support is provided for the view that in paradigms of the kind used here, allocation of attention to a psychologically defined hemispace is a more important factor in observed RT than structural links between stimulus and response mechanisms.     

Sequence effects in categorization of simple perceptual stimuli

Categorization research typically assumes that the cognitive system has access to a (more or less noisy) representation of the absolute magnitudes of the properties of stimuli and that this information is used in reaching a categorization decision. However, research on identification of simple perceptual stimuli suggests that people have very poor representations of absolute magnitude information and that judgments about absolute magnitude are strongly influenced by preceding material. The experiments presented here investigate such sequence effects in categorization tasks. Strong sequence effects were found. Classification of a borderline stimulus was more accurate when preceded by a distant member of the opposite category than by a distant member of the same category. It is argued that this category contrast effect cannot be accounted for by extant exemplar or decision-bound models of categorization. The effect suggests the use of relative magnitude information in categorization. A memory and contrast model illustrates how relative magnitude information may be used in categorization.     

Steady state responding based upon simple and compound stimuli

Two pigeons were trained to perform discrimination tasks along two dimensions, wavelength of a circular spot of light and orientation of a white line. Discriminability among stimuli along these dimensions was established for both subjects by means of a steady state testing procedure. The two dimensions were then combined by superimposing the white line upon the colored background. Subjects were given a series of tests in which a correct response could be made on the basis of either of the two components of the stimulus compounds. Discriminability among these redundant compound stimuli was found to be better than that among wavelength and tilt stimuli alone. A second series of tests was administered using both redundant and conflicting compound stimuli. The results of this test series are consistent with a response strategy in which subjects first examine both elements of a compound and then emit a choice response on the basis of the element that best predicts reinforcement.     

Visual working memory for simple and complex visual stimuli

Does the magical number four characterize our visual working memory (VWM) capacity for all kinds of objects, or is the capacity of VWM inversely related to the perceptual complexity of those objects? To find out how perceptual complexity affects VWM, we used a change detection task to measure VWM capacity for six types of stimuli of different complexity: colors, letters, polygons, squiggles, cubes, and faces. We found that the estimated capacity decreased for more complex stimuli, suggesting that perceptual complexity was an important factor in determining VWM capacity. However, the considerable correlation between perceptual complexity and VWM capacity declined significantly if subjects were allowed to view the sample memory display longer. We conclude that when encoding limitations are minimized, perceptual complexity affects, but does not determine, VWM capacity.     

Persistent and emergent cardiac responses elicited by simple stimuli

Heart rate and respiration were recorded as rabbits were exposed to visual and auditory events: light-on, light-off, light-change, noise-on, noise-off and noise-change. Each event lasted one second. One kind of stimulus event was presented ten times each session. Each kind of event was used for five sessions. On the following sessions (forty) two kinds of stimulus events were continued and used during the same session in order to introduce novelty. A beat-to-beat analysis of heart rate with corresponding respiration analysis showed (1) that rise and decay time of the reactions tended to decrease although magnitude might increase with repetition of the stimulus, (2) that some reactions elicited by some stimuli persisted beyond 400 trials, (3) that some reactions, not seen at first, appeared after 20–30 trials, (4) that respiration could be ruled out as a necessar causal factor for the heart rate changes, (5) that rate changes are specific to the modality or quality of the stimulus (e.g. noise-on vs. noiseoff or light-on), (6) that some reactions may be attenuated by stimulus novelty.     

Immediate and short memory: Recall of simple auditory stimuli

Experiments were carried out on conditions affecting the successful recall of simple, non-verbalised auditory stimuli. The effectiveness of recall of a given stimulus was measured by the ability to assess the pitch of one stimulus as compared to another stimulus presented after an interval of given length. The results indicate that the storage in memory of a simple auditory stimulus is possible, even in the case of pairs of stimuli separated in time by more than 5 min. In all experiments (stimuli differing by 2 semitones or by one semitone, and equal in intensity, or differing by ± 25 dB) the curve of errors shows a sharp increase when the interval between the two stimuli is 80 sec. It is possible that this sudden deterioration in the effectiveness of recall is connected with same alteration of the mechanism of memory. It is postulated that this alteration is due to a “switch-over” from immediate memory to short-term memory. The analysis of the errors shows that in certain circumstances there is a tendency towards a marked preponderance of errors resulting from underestimation rather than from overestimation of the first stimulus. This preponderance is obtained when we have pairs of equal loudness and it is even more marked when the first stimulus is softer than the second, and it is decreases when the first stimulus is louder than the second. These results suggest that in differentiating pitches of stimuli (in the 700–2000 Hz band) presented one after the other at certain fixed intervals of time, we are to find a phenomenon analogous to the classic time error found in estimations of loudness.     

Parallel processing of the attributes of single stimuli

Three experiments are described, in which Ss had to decide whether or not single stimuli, varying along the dimensions of shape and color, satisfied a given criterion. In different conditions, the number of dimensions relevant to the criterion was varied. The first experiment indicates that simple interpretations of a standard Nickerson procedure are potentially artifactual. In the last two experiments, a design involving different difficulties of discrimination was used so that a serial interpretation of the results could be convincingly rejected, even for unpracticed Ss. These results strongly support the view that perceptually parallel processing normally occurs in the identification of single multidimensional stimuli. By this interpretation, apparently similar tasks may produce different patterns of results because of the use of different decision processes by the Ss.     

The effect of frequency variation upon RT to the second of two shortly spaced auditory stimuli

A prepulse of a duration of 25 msec (S₁) was followed by an auditory reaction stimulus (S₂) requiring a binary choice.     

On the processing of simple visual and auditory stimuli at distinct levels

Two RT studies explored the possibility that identification of a single stimulus can take place through more than one perceptual route. In the first experiment, mean RT to color was systematically changed by varying type of catch stimulus. In the second experiment, the form of the RT distribution to a tone was changed by varying type of catch stimulus. Considerations of distribution means and shapes led to the conclusion that detection and discrimination are two of the alternative levels of perceptual processing which can be evoked in rapid identification of these stimuli.     

Search reaction time for single targets in multiletter stimuli with brief visual displays

The same set of Ss was run In an LT (single late target letter followed an earher multiletter display) and an ET (single early target preceded a later multiletter display) condition. On one-half the trials, the multiletter set included the target. and on the other half, the target was absent. The task of S was to push the “yes” (“no”) button if the target was present (absent), and reaction times were recorded. The most plausible processing model assumed that LT comparisons took place in a verbal-acoustic store and that ET comparisons took place in a visual store. It further assumed that processing within these stores was self-terminating, with rates that differed on “same” and “different” comparisons and which changed as the multiletter set increased. Classes of serial and parallel models that are falsified or supported by the present and similar data are discussed.     

Emergent simple discrimination in children: Preference for non-preferred stimuli

Previous research (Smeets, 1991) suggested that when given a new discrimination, children respond on the basis of physical similarity with previously discriminated stimuli. They respond to a stimulus similar to another preferred stimulus (S+ transfer) and respond away from a stimulus similar to another nonpreferred stimulus (S- transfer). When both types of transfer apply to the same stimulus, S+ transfer prevails, S+ Priority Transfer (S+PT). The present study demonstrated that S+PT also occurs when the criterion task consists of two nonpreferred stimuli. When given a choice between two previously nonpreferred stimuli, one similar and one dissimilar to other preferred stimuli, children select the first one. They do not so, however, when a nonpreferred stimulus resembling another preferred stimulus is presented with a new nonpreferred stimulus. These findings suggest that the children's preferences were not based on the physical resemblance with other (non)preferred stimuli but on the functions (S+, S-, S0) of individual stimulus components. A theoretical model is presented that accounts for all experimental data reported in the previous and present study. The model implies that discriminative responding not only results from but also determines the functional properties of individual stimulus elements.     

Key pecking under response-independent food presentation after long simple and compound stimuli

Sixteen pigeons were trained to peck a key using a response-independent (auto-shaping) procedure of food presentation. The 4-sec grain presentations were independent of responding but a keylight stimulus preceded each, with a 4-min interval between the grain presentation and the next stimulus. Subjects were divided into four groups, with two durations of the keylight (30 or 120 sec) and either one or four successive colors on the response key preceding food delivery. In Phase 2, the birds were continued with the same keylight duration but were presented the alternative number of key colors. All pigeons pecked the key during the stimulus. Birds in the two groups with the 30-sec stimulus duration began to respond significantly sooner than birds with the 120-sec duration. There were no significant differences in rate of pecking between groups by the last five days of Phase 1. In Phase 1, the pigeons exposed to the four stimulus components showed an increase in rate of pecking over the four components as grain presentation approached. The pigeons with one stimulus component did not exhibit this regularity. Analogous conditions in Phase 2 had similar results except for one group. The implications of the occurrence of key pecking due to response-independent food delivery for multiple and chained schedules were pointed out.     

Roles of the qualities and locations of stimuli and responses in simple associative learning

The Quality-Location Phenomenon is defined by the previous research of Lawicka (1964 and 1969) in which dogs easily learn go/no-go tasks to differences in stimulus quality and go-left/go-right tasks to differences in stimulus location whereas the opposite pairings of tasks and stimulus attributes are difficult to learn. The Lawicka-Konorski explanation in terms of drive differentiation and response selection is described, and a new hypothesis, the Quality-Location Hypothesis, is offered. This hypothesis states that the quality of a stimulus best serves as a cue for the quality of a response, whereas the location of a stimulus best serves as a cue for the location of a response. The evidence for the hypothesis is reviewed, and experimental considerations for its evaluation are mentioned.     

Affective synesthesia: Extracting emotion space from simple perceptual stimuli

Several experiments and reanalyses of archival data were performed in which sets of common emotions were mapped onto visual and auditory perceptual stimuli of varying degrees of complexity. Subjects showed reliability across several different experimental paradigms and diverse stimulus sets. Furthermore, the results were reducible to a two-dimensional emotion space of valence and activity, after the work of Osgood, Succi, and Tannenbaum (1957). The perceptual locus of an aesthetic stimulus in this two-dimensional space is hypothesized to provide a first approximation to how the synesthetic qualities of a percept provide a basis for emotional responses to such stimuli. More generally, this direct mapping of percept onto emotion provides an interesting conundrum for theories of emotion research.The author acknowledges support for this research from the ADAMA training grant, MH14257, Quantitative Methods for Behavior Research, University of Illinois, Department of Psychology. The work originated in conversations with Gerry Clore, whose encouragement and ideas were invaluable. Research assistant Kaarin Ryan provided invaluable help and ideas in the initial stages of this research. This paper is dedicated to Ned, Jeff, and Gordon.