Intact learning of new relations in amnesia as achieved through unitization

Abstract

Hippocampal amnesia is defined by deficits in the binding of relations among items--a deficit captured by the transverse patterning (TP) task. Unitization is a processing mechanism that may allow amnesic patients to compensate for relational memory deficits. Amnesic patient D.A. demonstrated intact TP, and performance was maintained 1 month following training. Successful acquisition of relations occurred only when D.A. fused or integrated objects into a unified representation. D.A. did not acquire relations when he did not generate such integrated scenarios, and acquisition of relations was slowed when integration had to occur for novel stimuli. Amnesic patients K.C. and R.F.R. were tested to provide comparative data; K.C. and R.F.R. did not benefit from unitization, perhaps due to additional cortical damage. We propose that unitization requires visual imagery of multiple items that are fused/integrated; through the benefit of extended on-line maintenance, this fused representation is anchored to existing representations in semantic memory.

Figure 1.

Stimuli and training procedures. a, Stimuli used for the Rock-Paper-Scissors, Playing Cards, Geometric Shapes, Abstract Objects, Geometric Shapes-Unitized, and Abstract Objects-Unitized conditions. Conditions that use objects and relations that were known before the experimental sessions, and before neurological insult for the amnesic patients, include RPS and Playing Cards. The Geometric Shapes and the Geometric Shapes-Unitized conditions used objects that were pre-experimentally known, but the relations among them were unknown. The Abstract Objects and the Abstract Objects-Unitized conditions used objects and relations that were pre-experimentally unknown. Therefore, the varieties of stimuli used allowed for any variations in TP performance to be examined when the objects and/or the relations were unknown before the experimental session. b, Training procedures. b, 1, Example stills from the flash animations that were shown before the training for the unitized conditions. Flash animations depicted one object physically interacting with the other object through the relations of squish, cover, or pierce. b, 2, Training procedures. Standard training presented two stimuli, one on each side of the screen, and participants were required to select the correct item that “wins. ” Responses are self-paced and feedback is provided. Unitized training proceeded in the same manner as standard training, except that a still image from the animation was included in the center of the stimulus display (“(U)”) to serve as “hint” for which stimulus was correct. Note that the stimuli are also shown by their corresponding letter (A–C, U) for ease of illustration; however, such letters were not presented to the participants. b, 3, Test procedures. All test blocks, regardless of whether training was standard or unitized, and regardless of whether the test was a pretest, immediate test, or 1-h-delay test, followed the same procedures and showed the same stimulus arrangement to the participants.

Figure 2.

TP performance for D.A. and K.C. (Sessions 1–3). Accuracy (percentage correct) on the no-feedback test conditions of transverse patterning (Rock-Paper-Scissors, Playing Cards, Geometric Shapes, and Abstract Objects) for amnesic patients K.C. and D.A. and control participants. The test condition was administered immediately following the training session, on which feedback was provided. Data from K.C. and the controls are re-presented from Moses et al. (2008). The 95% confidence interval is shown for the control mean. K.C. and D.A. were tested in each condition once in each of three separate sessions (Sessions 1–3). Control subjects were tested in a single session. Due to time constraints, D.A. was only able to complete the test sessions for RPS and Cards conditions in the first session. The dashed line denotes the 67% elemental maximum, indicative of an elemental strategy. The number beside the patient's initials corresponds to the testing session, as outlined in Table 5. D.A. and K.C. alike show predominantly intact TP for the conditions in which the objects and the relations among them were known before their neurological insults (RPS, Cards). By Session 3, D.A. also shows intact TP performance at immediate test for conditions in which the relations were unknown before his neurological insult (Geometric Shapes, Abstract Objects); whereas K.C. continued to show impaired performance.

Figure 3.

Predominantly intact TP performance for D.A. at immediate and 1-h-delay test (Sessions 4–7). a, b, Accuracy (percentage correct) on the no-feedback test conditions of transverse patterning (Rock-Paper-Scissors, Playing Cards, Geometric Shapes, and Abstract Objects) immediately following training (a) and following a 1 h delay (b) for amnesic patient D.A., R.F.R., and control participants. The 95% confidence interval is shown for the control mean. Procedures were the same as in Sessions 1–3, except for the inclusion in Sessions 4–7 of an additional test block that was provided at the 1 h delay. D.A. was tested in each condition once in each of the four separate sessions. R.F.R. was tested in Session 4 for the RPS and Shapes conditions only. Control participants were tested in a single session. The dashed line denotes the 67% elemental maximum, indicative of an elemental strategy. The number beside the patient's initials corresponds to the testing session, as outlined in Table 5. R.F.R. showed intact TP when the objects and the relations among them were known before his neurological insult (RPS), but impaired TP for the Geometric Shapes condition, which required learning of the relations among known objects. By contrast, D.A. showed intact TP for RPS and Cards (pre-experimentally known objects and relations), and showed intact performance by Session 5 for the Shapes condition (pre-experimentally known objects, but unknown relations), both immediately and following a 1 h delay. D.A.'s performance for the Abstract Objects (unknown objects, unknown relations) remained low following a 1 h delay.

Figure 4.

TP with and without Unitization procedures at immediate and 1-h-delay test for D.A., K.C., and R.F.R. (Sessions 8–10) Accuracy (percentage correct) on the no-feedback test conditions of transverse patterning that either did (Shapes-Unitized, Abstract-Unitized) or did not (Rock-Paper-Scissors, Shapes, Abstract Objects) employ unitization training procedures. a, b, Test conditions were presented immediately following training (a) and following a 1 h delay (b) for amnesic patients D.A., K.C., and R.F.R. D.A. and K.C. were tested in each condition once in each of three separate sessions. R.F.R. completed the immediate and 1-h-delay test for the Shapes and Shapes Unitized conditions in Session 8, and the immediate test of the Shapes-Unitized condition for Sessions 9 and 10 only. During training (feedback provided) in the Unitized sessions, the final still image of the two objects interacting was placed in the center of the display to serve as a guide for response selection, but during the test condition this center image was removed. The dashed line denotes the 67% elemental maximum, indicative of an elemental strategy. The number beside the patient's initials corresponds to the testing session, as outlined in Table 5. R.F.R. did not show improvements in TP under unitized training conditions at either immediate or 1-h-delay testing. D.A. showed intact TP for the Shapes-Unitized condition at immediate testing in Sessions 8–10, and at a 1 h delay by Session 10. D.A.'s performance on the Shapes condition (known objects, unknown relations) continued to remain high immediately and following a 1 h delay across Sessions 8–10, but performance on each of the Abstract Objects (unknown objects, unknown relations) conditions remained low at the 1 h delay, regardless of training procedures.

Figure 5.

Lasting TP performance for D.A. under unitization procedures following extended delays of 1 week and 1 month (Sessions 11–13). Accuracy (percentage correct) on the no-feedback test conditions of transverse patterning that either did (Shapes-Unitized, Abstract-Unitized) or did not (Rock-Paper-Scissors, Shapes, Abstract Objects) use unitization training procedures. a–c, Test conditions were presented to amnesic patient D.A. before any training (a; pretest following either a 1 week or 1 month interval from previous session), immediately following training (b) and following a 1 h delay (c). D.A. was tested in each condition once in each of three separate sessions. RPS was not given at pretest to not unduly influence performance on the other conditions through analogical transfer of the response scheme. Note that although the central unitized image was not provided during training for the Shapes-Unitized and Abstract-Unitized conditions of Sessions 12 and 13, the term Unitized here refers the manner of training provided in previous sessions. The dashed line denotes the 67% elemental maximum, indicative of an elemental strategy. The number beside the patient's initials corresponds to the testing session, as outlined in Table 5. In Session 11, D.A. demonstrated retention of the relations among objects for the Shapes and Shapes-Unitized conditions (known objects, unknown relations) following a 1 week delay. By Session 12, D.A. also exhibited intact TP and immediate and 1 h delays when Abstract objects were used (unknown objects, unknown relations), but only when unitization training procedures had been used. These gains in performance were maintained following a 1 month delay (Session 13).