Awareness of what is learned as a characteristic of hippocampus-dependent memory - PubMed (original) (raw)
Awareness of what is learned as a characteristic of hippocampus-dependent memory
Christine N Smith et al. Proc Natl Acad Sci U S A. 2018.
Abstract
We explored the relationship between memory performance and conscious knowledge (or awareness) of what has been learned in memory-impaired patients with hippocampal lesions or larger medial temporal lesions. Participants viewed familiar scenes or familiar scenes where a change had been introduced. Patients identified many fewer of the changes than controls. Across all of the scenes, controls preferentially directed their gaze toward the regions that had been changed whenever they had what we term robust knowledge about the change: They could identify that a change occurred, report what had changed, and indicate where the change occurred. Preferential looking did not occur when they were unaware of the change or had only partial knowledge about it. The patients, overall, did not direct their gaze toward the regions that had been changed, but on the few occasions when they had robust knowledge about the change they (like controls) did exhibit this effect. Patients did not exhibit this effect when they were unaware of the change or had partial knowledge. The findings support the idea that awareness of what has been learned is a key feature of hippocampus-dependent memory.
Keywords: amnesia; declarative memory; eye movements; medial temporal lobe.
Conflict of interest statement
The authors declare no conflict of interest.
Figures
Fig. 1.
Task design. In each of three test blocks, participants saw 24 color scenes (5 s per scene). Twelve scenes in block 1 were novel and were then repeated in blocks 2 and 3 (repeated scenes). Twelve other scenes in block 1 were novel, repeated in block 2, and then manipulated in a critical region in block 3 (manipulated scenes). No change occurred in the critical region of repeated scenes. The critical regions are identified by black squares (Right), but these squares did not appear during testing. The same testing sequence was repeated a second time with different scenes for a total of two sessions yielding 24 manipulated scenes and 24 repeated scenes.
Fig. 2.
Performance of controls (n = 6; white) and memory-impaired patients (n = 5; black). After viewing each scene in block 3, participants designated it as repeated or manipulated and then made a confidence judgment from 1 (maybe sure) to 3 (definitely sure). (A) The patients were impaired at discriminating between repeated and manipulated scenes. (B) Controls exhibited more confidence in their correct responses (C) than in their incorrect responses (I), but the patients did not. *P < 0.05. Error bars indicate SEM.
Fig. 3.
For each of 24 manipulated scenes, participants were designated as having robust knowledge about the manipulation (aware), as unaware, or as having intermediate knowledge. For each manipulated scene, participants first indicated whether the scene was manipulated (Y or N). Then, after being told that a manipulation had occurred, participants were asked to describe what had changed (Y, correct; N, incorrect) and to indicate the location of the manipulated region (Y, correct; N, incorrect). For example, Y/Y/Y indicates scenes where participants answered all of the questions correctly. Y/N/Y indicates that participants reported a manipulation had occurred, then could not describe what had changed, but correctly indicated where in the scene a change had occurred. The charts show the percentage of manipulated scenes in each category. There were no N/Y/N scenes.
Fig. 4.
Viewing of the manipulated (critical) region of manipulated scenes and the matched, unmanipulated (critical) region of repeated scenes. Controls (CON, n = 6) looked at the critical region of manipulated scenes more than they looked at the critical region of repeated scenes (i.e., the manipulation effect). Patients (MTL, n = 5) did not exhibit the manipulation effect. (A) The proportion of fixations in the critical region. (B) The proportion of time spent viewing the critical region. *P < 0.05. Error bars indicate SEM.
Fig. 5.
Viewing of the manipulated (critical) region of manipulated scenes when participants had robust knowledge (were aware) of the manipulation. The less aware condition includes scenes where participants were designated as either unaware (N/N/N in Fig. 3) or as having intermediate knowledge (such as Y/N/N or N/Y/Y in Fig. 3). CON (n = 6) and MTL (n = 5) exhibited the manipulation effect (i.e., manipulated > repeated) only when they were aware of the manipulation (mean = 14.5/24 scenes for CON and 3.3/24 scenes for MTL). (A) The proportion of fixations in the critical region. (B) The proportion of time spent viewing the critical region. *P < 0.05 versus the repeated scenes. Error bars indicate SEM.
Fig. 6.
Viewing of the manipulated (critical) region of manipulated scenes when participants (CON plus MTL, n = 11) were designated either as having robust knowledge (awareness) of the manipulation (Y/Y/Y in Fig. 3), as unaware (N/N/N), or as having intermediate knowledge (such as Y/N/N or N/Y/Y; see Fig. 3). Participants exhibited the manipulation effect (i.e., manipulated > repeated) when they were aware of the manipulation but not when they were unaware or when they had partial knowledge about the manipulation. (A) The proportion of fixations in the critical region. (B) The proportion of time spent viewing the critical region. *P < 0.05 versus the repeated scenes. Error bars indicate SEM.
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