Biomedical subjects

I G Dobbins

Publications and source records attributed to I G Dobbins.

7 recordsLinked to original sources

PubMed2001

Visual implicit memory in the left hemisphere: evidence from patients with callosotomies and right occipital lobe lesions.

Identification of visually presented objects and words is facilitated by implicit memory for past visual experiences with those items. Several behavioral and neuroimaging studies suggest that this form of memory is dependent on perceptual processes localized in the right occipital lobe. We tested this claim by examining implicit memory in patients with extensive right occipital lobe lesions, using lexical-decision mirror-reading, picture-fragment, and word-fragment-completion tests, and found that these patients exhibited normal levels of priming. We also examined implicit memory in patients with complete callosotomies, using standard and divided-visual-field word-fragment-completion procedures, and found that the isolated left hemisphere exhibited normal priming effects. The results indicate that the right occipital lobe does not play a necessary role in visual implicit memory, and that the isolated left hemisphere can support normal levels of visual priming in a variety of tasks.

Adult↗

PubMed2001

The systematic discrepancy between A' for overall recognition and remembering: a dual-process account.

Signal detection accounts of recognition assume that all item endorsements arise from the assessment of a single continuous indication of memory strength, even when subjects claim to categorically separate items accompanied by contextual recollection from those that are not (viz., remembering vs. knowing). Dissociations of these response types are held to occur because the former require a higher response criterion for item strength than does the latter. Meta-analytic and individual subject data suggest that when the A' metric is used, accuracy for remembering can systematically deviate from that of overall responding for individual subjects. This occurs because, unlike the symmetric and rigid receiver-operating characteristic (ROC) implied under A', empirical ROCs are asymmetric and plastic. A dual-process model predicted that the magnitude of the deviation would vary as a systematic function of the proportion of overall recognition accompanied by subjective remember reports for individual subjects. The predictions were confirmed using multiple regression on Monte Carlo and experimental data sets and were also shown to generalize to the double equal-threshold, single high-threshold [i.e., H - FA; (H - FA)/(1 - FA)], and the equal variance signal detection d' corrections. The unequal variance signal detection model was also shown to mirror the data, but only under the post hoc assumption that every subject adopts a very similar remember criterion placement rule. The results demonstrate that the systematic failure of tightly constrained models of recognition constitutes valuable regression data for more complex models and simultaneously highlights why single-point measures of accuracy are unsuitable as summaries across conditions or groups. Furthermore, the results show that remember rates carry unique information regarding the underlying processes governing individual subject performance that cannot be gleaned from the overall hit and false alarm rates in isolation.

Data Interpretation, Statistical↗

PubMed2000

The contribution of recollection and familiarity to yes-no and forced-choice recognition tests in healthy subjects and amnesics.

Recent reports suggest that some amnesic patients perform relatively normally on forced-choice recognition memory tests. Their preserved performance may reflect the fact that the test relies more heavily on assessments of familiarity, a process that is relatively preserved in these patients, than do other recognition tests such as yes-no tests, which may rely more on recollection. The current study examined recognition memory using yes-no and forced-choice procedures in control and amnesic patients in order to determine whether the two tasks differentially relied on recollection and familiarity, and whether the extent of the recognition memory deficit observed in amnesia was dependent upon the type of recognition test used to measure performance. Results using the remember-know procedure with healthy subjects showed that there were no substantial differences in recognition accuracy or in the contribution of recollection to these two tasks. Moreover, amnesic patients were not found to perform better on a forced-choice test than on a yes-no test, suggesting that familiarity contributed equally to these two types of recognition test.

Adolescent↗

PubMed2000

Predicting individual false alarm rates and signal detection theory: a role for remembering.

The relationships between hit, remember, and false alarm rates were examined across individual subjects in three remember-know experiments in order to determine whether signal detection theory would be consistent with the observed data. The experimental data differed from signal detection predictions in two critical ways. First, remember reports were unrelated, or slightly negatively related, to the commission of false alarms. Second, both response types (remembers and false alarms) were uniquely related to hit rates, which demonstrated that the hit rate cannot be viewed as the result of a single underlying strength process. These results are consistent with the dual-process signal detection model of Yonelinas (1994), in which performance is determined by two independent processes--retrieval of categorical context information (remembering) and discriminations based on continuous item strength. Remember and false alarm rates selectively tap these processes, whereas the hit rate is jointly determined. Monte Carlo simulations in which the dual-process model was used successfully reproduced the pattern in the experimental data, whereas simulations in which a signal detection model, with separate "old" and "remember" criteria, was used, did not. The results demonstrate the utility of examining individual differences in response types when one is evaluating memory models.

Adult↗

PubMed1999

Recognition memory for faces: when familiarity supports associative recognition judgments.

Recognition memory for single items can be dissociated from recognition memory for the associations between items. For example, recognition tests for single words produce curvilinear receiver operating characteristics (ROCs), but associative recognition tests for word pairs produce linear ROCs. These dissociations are consistent with dual-process theories of recognition and suggest that associative recognition relies on recollection but that item recognition relies on a combination of recollection and assessments of familiarity. In the present study, we examined associative recognition ROCs for facial stimuli by manipulating the central and external features, in order to determine whether linear ROCs would be observed for stimuli other than arbitrary word pairs. When the faces were presented upright, familiarity estimates were significantly above zero, and the associative ROCs were curvilinear, suggesting that familiarity contributed to associative judgments. However, presenting the faces upside down effectively eliminated the contribution of familiarity to associative recognition, and the ROCs were linear. The results suggest that familiarity can support associative recognition judgments, if the associated components are encoded as a coherent gestalt, as in upright faces.

Adult↗

PubMed1998

Unilateral medial temporal lobe memory impairment: type deficit, function deficit, or both?

Previous research has characterized memory deficits resulting from unilateral hippocampal system damage as 'material specific', suggesting that left damage results in verbal memory impairment with preservation of visuospatial function and the converse with right damage. Implicit within this hypothesis are the assumptions that the systems are independent and memory is lateralized for each type of material. To test the verbal component of this hypothesis, unilateral hippocampal lesion and commissurotomy patients were compared with controls on a multiple-list free-recall task. The material specific hypothesis predicts severe impairment only with left lesions; right lesions and commissurotomy patients should be only minimally impaired. However, secondary memory was compromised at immediate recall for all patient groups, with both unilateral groups showing comparable and severe verbal episodic memory deficits. Final testing across all lists also revealed severe impairment in commissurotomy patients. Finding both unilateral groups to be similarly impaired for verbal material is taken as evidence against a material specific deficit during this verbal episodic memory task. Although previous data suggest that left patients are considerably more impaired during some verbal tasks, this may not be specific to the material, but rather the combination of material and task demands. Implications for the material specific hypothesis are discussed.

Adult↗

PubMed1998

Confidence-accuracy inversions in scene recognition: a remember-know analysis.

S. E. Clark (1997) offered a modified signal-detection explanation of the confidence-accuracy inversions observed in E. Tulving's (1981) experiments. In addition to replicating E. Tulving (1981), we had participants make "remember-familiar" judgments. Confidence and accuracy dissociated across subjective reports. Response confidence differed only for judgments based on familiarity, whereas accuracy differed only for "remember" responses. S. E. Clark's model does not predict this, nor can it mimic "remember" performance across all conditions. We propose that although "knowing" can be accommodated within an equal variance signal-detection account, "remembering" is governed by contextual constraints that influence the distinctiveness of information upon which participants rely during reports. The current paradigm is a pictorial analogue to H. L. Roediger and K. B. McDermott's paradigm (1995) in that participants claim to explicitly remember thematically related items that were not actually seen during study.

Humans↗