Takeo Isarida

A user authentication system using schema of visual memory

On many image-based user authentication systems, they have to present a user’s pass-image on their display at each authentication trial, so they can be vulnerable against an observing attack. This paper proposes a user authentication system using “unclear images” as pass-images, in which only the legitimate users are allowed to see the original images corresponding to the unclear pass-images in the enrollment phase. The legitimate users can easily remember their unclear pass-images by using the original images as clues, while illegal users without the clues have difficulties to find out and remember the other user’s unclear pass-images.

Environmental context effects of background color in free recall

In four experiments, we investigated background-color context effects in free recall. A total of 194 undergraduates studied words presented one by one against a background color, and oral free recall was tested after a 30-sec filled retention interval. A signal for recall was presented against a background color throughout the test. Recalled items were classified as same- and different-context items according to whether the background colors at study and test were the same or different. Significant context effects were found in Experiments 1 and 2, in which two background colors were randomly alternated word by word. No context effects were found in Experiments 3 and 4, in which a common background color was presented for all items (Experiment 3) or for a number of successive items (Experiment 4). The results indicate that a change in background colors is necessary and sufficient to produce context effects. Implications of the present findings are discussed.

Effects of environmental context manipulated by the combination of place and task on free recall

Three experiments, using a 2 (study context) × 2 (test context) between‐subjects design, were conducted to examine the effects of environmental context manipulated by the combination of two contextual elements, place and task, on free recall. Undergraduates individually studied nouns and received a free‐recall test, with a 10‐minute filled retention interval. The contexts were manipulated by the combination of task and place in Experiment 1, by place alone in Experiment 2, and by task alone in Experiment 3. For the manipulation of place and task, two perceptually distinctive places and two distinctive tasks (a calculation task and a fine‐motor task) were used. Tasks were imposed before and after studying target items and before a free‐recall test. Significant environmental‐context effects were yielded in Experiment 1, but not in the other experiments. The implications of the results are discussed.

Odor-context effects in free recall after a short retention interval: A new methodology for controlling adaptation

The present study investigated context effects of incidental odors in free recall after a short retention interval (5 min). With a short retention interval, the results are not confounded by extraneous odors or encounters with the experimental odor and possible rehearsal during a long retention interval. A short study time condition (4 s per item), predicted not to be affected by adaptation to the odor, and a long study time condition (8 s per item) were used. Additionally, we introduced a new method for recovery from adaptation, where a dissimilar odor was briefly presented at the beginning of the retention interval, and we demonstrated the effectiveness of this technique. An incidental learning paradigm was used to prevent overshadowing from confounding the results. In three experiments, undergraduates (N = 200) incidentally studied words presented one-by-one and received a free recall test. Two pairs of odors and a third odor having different semantic-differential characteristics were selected from 14 familiar odors. One of the odors was presented during encoding, and during the test, the same odor (same-context condition) or the other odor within the pair (different-context condition) was presented. Without using a recovery-from-adaptation method, a significant odor-context effect appeared in the 4-s/item condition, but not in the 8-s/item condition. Using the recovery-from-adaptation method, context effects were found for both the 8- and the 4-s/item conditions. The size of the recovered odor-context effect did not change with study time. There were no serial position effects. Implications of the present findings are discussed.

Influences of environmental context on the recency effect in free recall

A total of 208 undergraduate participants incidentally encoded a list of seven pairs of familiar words in two experiments. A 30-sec calculation task was imposed before and after each pair was encoded. Participants received a free recall test 24 h (Experiment 1) or 10 min (Experiment 2) after the encoding session, under conditions in which the original environmental context was reinstated or not. The environmental context was manipulated in terms of the combination of the physical features of the room, the subsidiary task conducted, the experimenter (Experiment 1), or background music (Experiment 2). A recency effect appeared when the original environmental context was reinstated in both experiments, even though the IPI/RI ratio was too small to produce recency effects according to the ratio rule. The results imply that the environmental context should be taken into account for the recency effect.

Effects of simple- and complex-place contexts in the multiple-context paradigm

In four experiments, a total of 384 undergraduates incidentally learned a list of 24 nouns twice in the same context (same-context repetition) or different contexts (different-context repetition). Free recall was measured in a neutral context. Experiments 1, 2, and 3 used a context repetition (same- or different-context repetition) × inter-study and retention intervals (10 min or 1 day) between-participants design. Context was manipulated by the combination of place, social environment, and encoding task (Experiment 1), place and social environment (Experiment 2), or place alone (Experiment 3). Experiment 4 used a context repetition × type of context (context manipulated by place or by place, social environment, and encoding task) between-participants design, with a 10-min inter-study interval and a one-day retention interval. The present results indicate that the determinant of the superiority of same- or different-context repetition in recall is the type of context. Implications of the results were discussed.

Context-dependent effects of background colour in free recall with spatially grouped words

Three experiments investigated context-dependent effects of background colour in free recall with groups of items. Undergraduates (N=113) intentionally studied 24 words presented in blocks of 6 on a computer screen with two different background colours. The two background colours were changed screen-by-screen randomly (random condition) or alternately (alternation condition) during the study period. A 30-second filled retention interval was imposed before an oral free-recall test. A signal for free recall was presented throughout the test on one of the colour background screens presented at study. Recalled words were classified as same- or different-context words according to whether the background colours at study and test were the same or different. The random condition produced significant context-dependent effects, whereas the alternation condition showed no context-dependent effects, regardless of whether the words were presented once or twice. Furthermore, the words presented on the same screen were clustered in recall, whereas the words presented against the same background colour but on different screens were not clustered. The present results imply: (1) background colours can cue spatially massed words; (2) background colours act as temporally local context; and (3) predictability of the next background colour modulates the context-dependent effect.

Reexamination of mood-mediation hypothesis of background-music-dependent effects in free recall

The present study reexamined the mood-mediation hypothesis for explaining background-music-dependent effects in free recall. Experiments 1 and 2 respectively examined tempo- and tonality-dependent effects in free recall, which had been used as evidence for the mood-mediation hypothesis. In Experiments 1 and 2, undergraduates (n = 75 per experiment) incidentally learned a list of 20 unrelated words presented one by one at a rate of 5 s per word and then received a 30-s delayed oral free-recall test. Throughout the study and test sessions, a piece of music was played. At the time of test, one third of the participants received the same piece of music with the same tempo or tonality as at study, one third heard a different piece with the same tempo or tonality, and one third heard a different piece with a different tempo or tonality. Note that the condition of the same piece with a different tempo or tonality was excluded. Furthermore, the number of sampled pieces of background music was increased compared with previous studies. The results showed neither tempo- nor tonality-dependent effects, but only a background-music-dependent effect. Experiment 3 (n = 40) compared the effects of background music with a verbal association task and focal music (only listening to musical selections) on the participants’ moods. The results showed that both the music tempo and tonality influenced the corresponding mood dimensions (arousal and pleasantness). These results are taken as evidence against the mood-mediation hypothesis. Theoretical implications are discussed.