Immediately preceding stimuli increase the detection of a less detectable but not a more detectable stimulus

Grouping and Assimilation in Perception, Memory, and Conditioning

A group-assimilation theory hypothesizes that a Gestalt-like group is associated with assimilation among the parts of the group. Assimilation is an increase in the perceived or sensed similarity of 1 part to a 2nd part. Assimilation occurs for traditional parts such as color but also occurs for salience. The theory accounts for key outcomes in perception, memory, and conditioning. An important hypothesis is that traditional assimilation and salience assimilation tend to have opposing effects on identification. The traditional assimilation of a target to a 2nd part frequently impairs the target's identification. In contrast, the assimilation of a less salient target to a more salient 2nd part increases the salience of the target and thus improves the target's identification. The corresponding hypothesis that 2 groups are associated with contrast between those parts that belong to different groups is also considered.

The Weber fraction versus perceived similarity

The Weber fraction type of discrimination outcome means that stimuli of high magnitude are difficult to discriminate. Simultaneous and successive discriminations between two long (high magnitude) lines and also between two short (low magnitude) lines were carried out. Over-all performance on the successive discrimination between the two long lines was much poorer than on the three other discriminations. This discrimination also produced the poorest performance on different stimuli relative to same stimuli. The latter result should indicate that the two successive long lines were perceived as most similar. These and additional results support the conclusion that over-all discrimination performance and perceived similarity were consistently associated even though they were not consistently associated with length and time of occurrence (simultaneous versus successive). Nevertheless, the association of discrimination with perceived similarity has received minimal attention in the psychophysics area.

Sentences and rehearsals increase rated similarity: support for assimilation-in-salience theory

The present study concerns how organization produces good retention. Exp. 1 indicated that college students rated two words in sentences as more similar than the same two words alone. In Exp. 2 they rated the two words of old presumably rehearsed pairs as more similar than the two words of new pairs. A sentence is a type of organization, and words that are rehearsed together are frequently subjectively organized. Therefore, the two experiments suggest that organized stimuli also assimilate among themselves (and evidence in the literature concurs). Organized stimuli also produce a highly salient (activated) single memorial group (unit) such as the meaning that a simple sentence comes to have according to evidence in the literature. So, the two experiments support the hypothesis that organized stimuli produce good retention, assimilation among themselves, and a highly salient group. Consequently, organized stimuli may also assimilate to the highly salient group and thereby increase in salience, with this increase enabling the good retention. This assimilation-in-salience theory of how organization produces good retention accords with perceptual evidence suggesting that a target increases in salience through its assimilation to a more salient simultaneously present context.

Assimilation in visibility: additional evidence

The present research tested the theory that a less visible target increases in similarity to a more visible simultaneous context, and that therefore the target increases in visibility. This assimilation-in-visibility theory was tested using context + targets that were either 3-line brackets or 2-line right angles, contexts and targets that were the component lines of these context + targets, with the target always the identical single top line. Experiments with a total of 204 participants indicated that the 3-line context + targets resulted in better context + target versus context discriminations than target versus background discriminations than did the 2-line context + targets. This was so for both over-all errors and misses but not false alarms. It is concluded that only the 3-line context + targets increased the visibility of the 1-line target. Additional analysis indicated that the 2-line contexts of the 3-line context + targets were more visible than all the 1-line stimuli. So, the 1-line target assimilated to a simultaneous more visible 2-line context and thereby increased in visibility, thus improving the context + target versus context discrimination. This support for the assimilation-in-visibility theory is of interest because assimilation and contrast in visibility may play a large role in perception.

Discrimination learning decreases perceived similarity according to an objective measure

Initial identification discriminations between two sizes and between two slants produced better overall performances on subsequent size and slant same-different discriminations, respectively. This size- and slant-specific transfer was due to an improvement on only the different pairs. Time-duration identification discriminations with the identical stimuli and response assignments improved neither overall same-different performances nor performances on different pairs. A good performance on different pairs relative to same pairs should indicate a low perceived similarity. The literature indicates that A-X and B-Y pairings produce a positive transfer on an A-versus-B discrimination when X and Y are relatively low in similarity, and also indicates that a low perceived (not physical) similarity improves discrimination learning. An increase in salience should have also improved performance on the same pairs.

THE CONCLUSION

the initial discriminations decreased the perceived similarity of parts (size or slant). This decrease resembles perceptual contrast. A discrimination between two parts also seems to increase the extent to which each part is apprehended as a separate group. Therefore, the conclusion accords with the position that two groups are associated with contrast, including for visibility.