Pleasant vs. Unpleasant Stimuli on Free Recall

¶ … Pleasant vs. Unpleasant Stimuli on Free Recall

Memory is a mental process where information is encoded, stored, and then retrieved at sometime in the future. There is the great deal of research attempting to ascertain what particular factors associated with the stimuli to be remembered and with the emotional state of the learner either increase or decrease the amount of material recalled during learning trials. One factor that has been manipulated is whether or not the material to be learned is judged to consist of either pleasant or unpleasant stimuli. Of course this judgment is often an individual one, but the researchers have attempted to use stimuli that are normally judged to be either pleasant or unpleasant or have been normed on these attributes to determine the effects of pleasantness on recall for material to be learned. The current study attempted to replicate the findings that recall material is greater when the content of the material is associated as being pleasant vs. material that is associated as being emotionally unpleasant in a sample of college students. The findings of this study are consistent with the overall findings in the research. The results are discussed in the context of the methodology used, inferences that can be made from the findings, how the current findings suggest that individuals should approach learning situations, and directions for future research.

Memory refers to a mental process where information is encoded, stored, and retrieved for use (Atkinson & Shiffrin, 1968). The early stage models of memory conceptualized a process beginning at the sensory stage (with a very short duration large capacity) moving into short -- term memory (with a limited duration and limited capacity), and humility in long-term storage (typically believed to be unlimited in both duration and capacity; Reisberg, & Snavely, 2010). While these early stage models have been expanded, their basic premises remain valid (Christianson, 2014). One important issue that has often surfaced in the research as that the process of memory is not, contrary to what many believe, like a tape recorder that accurately records events as they are presented in the environment. Instead, our recollection of events is pliable and subject to a number of influences (e.g., Loftus, 1979).

In order for people to form memories, information must transverse through several phases/stages (Christianson, 2014). Transitioning from one stage to another requires a different process depending on the stage. For example, in order to single out relevant information in sensory storage one must pay attention to it; in order to retain information in short -- term memory one must use some form of rehearsal; and in order to transfer information into long-term storage one must use some form of encoding strategy that might involve rehearsing or conceptualizing information (Domjain, 2004). While sensory storage is considered to have a large capacity and is specific to the sensory domain (e.g., sight, sound, etc.), short-term memory has a much more limited capacity commonly cited as "7 ± 2" chunks of information (Miller, 1956). More recent conceptualizations of short-term memory include the model of working memory Baddeley & Hitch, 1975). While the terms working memory and short-term memory are often used interchangeably, working memory refers to the structures and processes that occur in short-term memory designed to temporarily store and manipulate information. Baddeley and Hitch (1975) refer to these processes as the visuospatial sketchpad (for images and other visual information), a phonological loop (for use with verbally mediated information), and an executive control system that manages these and coordinates the processes when more than one system must be used simultaneously. In addition, the major components of the visuospatial sketchpad and phonological loop also have subdivisions making the concept of working memory quite complex. Many of the stimuli that we attempt to encode have both visual and language-based features to them and therefore tax all aspects of working memory (Christianson, 2014).

Long-term memory is also no longer considered to be a singular construct (Christianson, 2014). The first major distinction that has been made in long-term memory is whether the memories in this type of storage are consciously accessible, that there is a need for conscious recollection or recall when reproducing these memories (in other words these memories would be part of the controlled processes in a dual-process model of cognition that divides cognitive processes based on several attributes such as their speed, access to consciousness, etc.; Christianson, 2014). Memories that are consciously accessible have been termed declarative or explicit memory (Christianson, 2014). Memories that are not consciously accessible have been termed non- -- declarative memory or implicit memory (this division would consist of automatic processes according to the dual -- process model of cognition; Christianson, 2014). Declarative and non-declarative memory are further divided into several subdivisions.

In order to become registered in long -- term memory information must first be retained in short-term or working memory. Because short-term memory has a limited capacity and duration one can adopt different strategies in order to maximize its potential. Likewise, certain forms of information may further limit the capacity of short-term memory. There are several different hypotheses as to why this is so. One popular hypothesis is that because short-term memory has limited resources, vague or less salient types of information are not activated as strongly as more concrete and salient types of information are (Just & Carpenter, 1992). In addition, it is been hypothesized that processes such as interference and decay are especially prominent with regard to working memory due to its well -- defined limited capacity (Towse, Hitch, & Hutton, 2000). Thus, information that can be conceptualized or tied to past experience has an automatic advantage when one is attempting to retain it in short -- term memory. Very abstract concepts or concepts that are not readily activated by both the visuospatial sketch pad and the phonological loop in working memory should even further limit the capacity and duration of short-term memory (Paap, Newsome, McDonald, & Schvaneveldt, 1982). Thus, understanding how different types of stimuli are encoded in retain in memory can offer a great deal of insight into the memory process itself. One of the areas of this research involves how the effects of emotionally charged stimuli or personal judgments regarding whether the stimuli is likeable (pleasant or unpleasant) affect recall.

From an evolutionary perspective, it would appear to be adaptive for memory for stimuli perceived as pleasing or pleasant to be enhanced, because these stimuli are often more important regarding survival and reproduction than are unpleasant or neutral stimuli (e.., food, potential partners, etc.). Research also suggests that stimuli that produce judgments such as being pleasant or unpleasant move through the brain in parallel with systems that are allocated towards attention (Christianson, 2014). Since attention is not a global process it may well be that the arousal associated with these judgments helps individuals maintain a readiness to respond to situations. There are other factors that can confound this relationship, such as age; however, emotionally charged events and affective judgments of stimuli being either pleasant or unpleasant are remembered better than neutral ones (Christianson, 2014).

It also appears that memories are treated differently in the brain when associated by pleasant emotions or unpleasant emotions or judgments regarding the pleasantness of stimuli (Christianson, 2014) such that information in memory is retained differently depending on whether it is associated as being pleasant or unpleasant (Christianson, 2014). Overall it appears that stimuli judged to be pleasant (or positive memories) contain more contextual details which help them to be encoded, consolidated, and stored in memory more efficiently than do negative (unpleasant) and neutral stimuli (Christianson, 2014).

For example, Bradley, Greenwald, Petry, and Lang (1992) tested 89 students' recall of 60 pictures that were either rated as moderately or highly pleasant or unpleasant. The nature of the pictures was rated on such qualities as valence and arousal. A free recall test was a performed immediately following the presentation of the 60 pictures and 59 of the 89 students were contacted again a year later and given a delayed recall test. Results indicated that in the free recall condition the pictures rated as either moderately or highly pleasant or recall with greater frequency than pictures rated as either moderately or highly unpleasant. However, following a year delay there was an interaction such that the moderately pleasant pictures were recalled only slightly more often than the moderately unpleasant pictures, whereas pictures rated as highly unpleasant were recalled slightly more often than pictures rated as highly pleasant. The differences between the two (pleasant and unpleasant) were not significant in either the moderately or highly pleasant/unpleasant conditions during the long-term recall conditions; however in the immediate recall condition these differences were highly significant, suggesting that the effect of emotional valence may only be important during encoding.

Recognition memory differs from free recall in that during recognition one does not need to actually retrieve stored information but only associate it with past experience (Christianson, 2014). Researchers have tested whether emotional valence affects recognition memory as well. Fernandez-Rey and Redondo (2007) randomly presented 193 volunteers (137 females and 56 males) rate 36 emotionally provocative pictures. The pictures were selected from the International Affective Picture System and chosen on the basis pleasantness (high, low) and arousal (high, low). In the first portion of the experiment the participants rated the pictures on their emotionality (pleasantness) and arousal. Then the participants returned two months later and engaged in a recognition memory task for the 60 pictures. Pictures judged as being highly arousing or were recognized better than pictures judged as not being arousing (low pleasantness). Recognition was better for pictures judged to be highly pleasant than those not pleasant or low in pleasantness, consistent with previous findings. Thus, while the emotional valence associated with stimuli (high pleasantness vs. low pleasantness) did not affect long-term free recall significantly (Bradley et al., 1992) it did appear to have an effect on recognition trials. Pleasant stimuli were recognized significantly better than neutral or unpleasant stimuli.

However, the findings that memory for positive/pleasant stimuli is greater than memory for negative/unpleasant stimuli is not always replicated and a number of different variables can affect these outcomes such the age of the participants. For example, Comblain, D'Argembeau, and Van der Linden 2005) had 80 adults (40 younger participants with a mean age of 22.1 and 40 older adults with a mean age of 63.5) complete questionnaires regarding specific types of memories. The participants were to recall several different types of memories. The memories had to be two positive or pleasant, to negative or unpleasant, and two that were neutral regarding how pleasant they were. These had to be specific events that occurred within the previous five years and were at least six months old. For each event the participants were asked to think about the event for a few minutes and to try to remember it as clearly as possible before completing the questionnaire. The memories were rated on 16 dimensions drawn from the Memory Characteristics Questionnaire. Findings indicated that greater vividness of recall was associated with unpleasant memories in older adults, whereas this finding was not replicated in the younger sample.

The current study attempted to replicate the finding that recall for visual stimuli that are judged to be pleasant would be greater than for visual stimuli rated as not being pleasant for short-term recall in a small sample of college students.

Method

Participants. There were eleven students from xxx who participated in this experiment (N = 11). All of the students were enrolled in a General Psychology Research Method class.

Apparatus. Twenty 8x10 pictures containing ten pleasant depictions and ten unpleasant depictions were used. There were verbal instructions given, and the pictures were taken from xxx.

Procedure. The experimenter randomly displayed the pictures to the subjects. All subjects were told to view each picture, and write down as many as they could recall. All subjects were given as much time needed to complete the task. The number of correct responses was tabulated for all subjects.

Results

The mean number of pleasant stimuli recalled by all of the subjects was 8.00. The mean number of unpleasant stimuli recalled was 6.72. It appears from the data that the numbers of pleasant stimuli were better recalled than the number of unpleasant stimuli.

Discussion

The current study investigated how the ability to visualize concepts and information deemed as either being pleasant or unpleasant contribute to the ability to encode information. In the current study the participants were presented with 20 pictures; 10 deemed as pleasant scenes and 10 deemed as being unpleasant. It was hypothesized that the details from the more pleasant scenes would be immediately recalled at a greater rate than the more unpleasant scenes. The pleasant scenes were believed to engage more aspects of working memory to allow the participants to better form a visual impression of the scene and therefore allow participants to retain information longer and working memory (Towse et al., 2000).

The hypothesis of this experiment was supported. Moreover, the capacity of working memory of the participants in this experiment was consistent with the traditional notion of "7 ± 2" chunks of information for both pleasant and unpleasant scenes. Thus based on these findings, while pleasant scenes are recalled easier than unpleasant ones, the emotional reaction of a visual stimulus does not appear to significantly lead to an overall increase or decrease in working memory capacity for pleasant or unpleasant stimuli.

There are several practical applications to be gathered from this study. First, making information relevant and multi-modal (e.g., conceptualizing information using as many senses as possible such as visual aspects and emotional valance) should make information easier to learn. Information judged as being pleasant would be retained better than information judged as being unpleasant.

Secondly, attaching meaning to information as opposed to attempting to use a rote strategy should result in better recall for information. Third, trying to understand why and how things are related should engage more aspects of memory and result in better recall for material.

Finally, because working memory and short-term memory are limited in their abilities and capacities it is important not to overlook them. Trying to learn information while multitasking or watching television would not be as effective as concentrating on the information in trying to draw relationships between concepts. We would suspect that given the amount of information recalled in both conditions of this experiment was near the upper limit of working memory capacity that distractions such as a television or engaging the participants in another task during learning would decrease the overall amount of material recalled in both conditions.