Delay Discounting and the Cost of Waiting

<p>If offered $50 now or $100 in a year, many of us will choose $50 now. This occurs because of delay discounting – the idea that reinforcers lose value over time. Individuals tend to display shallower discounting (self-controlled decision-making) in hypothetical discounting tasks, and steeper discounting (impulsive decision-making) in experiential discounting tasks. Hypothetical discounting tasks involve participants making a series of hypothetical monetary decisions (e.g. $50 now versus $100 in a year) over a range of delays. Experiential discounting tasks involve participants experiencing the delays and outcomes of their choices. A critical difference between hypothetical and experiential discounting tasks is the type of delay they use. Hypothetical discounting task delays typically involve postponing. This involves participants imagining the reward is delivered to them after the delay and that they are free to pursue other activities during the delay. Experiential task delays involve participants waiting out each delay before they receive their reward, (unable access any alternative reinforcement during the delay). Individuals discount more steeply when tested experientially than hypothetically. Experiment 1 investigated whether waiting and postponing are different discounting constructs. We achieved this via a 2 X 2 within-subjects design where both experiential and hypothetical discounting tasks had both Waiting and Postponing conditions. The hypothetical discounting task involved participants being instructed to imagine waiting for a reward after a delay (Waiting Condition), or imagine the reward would simply be delivered to them after the delay (Postponing Condition). The experiential task involved participants playing a video game that involved having to stop playing and wait for a larger number of points after a delay (Waiting Condition), or playing the game and getting the points delivered after the delay (Postponing Condition). We expected steeper discounting rates when waiting compared to postponing in both the experiential and hypothetical tasks. We found this effect only in the hypothetical task; however, this might be due to our procedure. We randomised the waiting and postponing trials in both tasks and this may have resulted in the participants being unable to discriminate between the interspersed trials. Experiment 2 investigated whether this methodological feature affected discounting in the experiential task, and we found that blocking the trials resulted in the anticipated effect. We found steeper discounting in both the experiential and hypothetical tasks for waiting compared to postponing after implementing this change, suggesting that waiting and postponing are different constructs. Experiment 3 investigated what drives the difference between waiting and postponing. We found that waiting has a greater effect on reward value than postponing due to the inability to access alternative reinforcement during the delay. We also investigated the relationships among our discounting measures and a measure of the consideration of future consequences, and a measure of delayed gratification. We found no correlation among discounting and these measures, and no consistent correlation between waiting and postponing. Overall, our results indicated that waiting and postponing are distinct constructs, and that the inability to access alternative reinforcement during a delay is the key difference between them.</p>

Delay Discounting and the Cost of Waiting

<p>If offered $50 now or $100 in a year, many of us will choose $50 now. This occurs because of delay discounting – the idea that reinforcers lose value over time. Individuals tend to display shallower discounting (self-controlled decision-making) in hypothetical discounting tasks, and steeper discounting (impulsive decision-making) in experiential discounting tasks. Hypothetical discounting tasks involve participants making a series of hypothetical monetary decisions (e.g. $50 now versus $100 in a year) over a range of delays. Experiential discounting tasks involve participants experiencing the delays and outcomes of their choices. A critical difference between hypothetical and experiential discounting tasks is the type of delay they use. Hypothetical discounting task delays typically involve postponing. This involves participants imagining the reward is delivered to them after the delay and that they are free to pursue other activities during the delay. Experiential task delays involve participants waiting out each delay before they receive their reward, (unable access any alternative reinforcement during the delay). Individuals discount more steeply when tested experientially than hypothetically. Experiment 1 investigated whether waiting and postponing are different discounting constructs. We achieved this via a 2 X 2 within-subjects design where both experiential and hypothetical discounting tasks had both Waiting and Postponing conditions. The hypothetical discounting task involved participants being instructed to imagine waiting for a reward after a delay (Waiting Condition), or imagine the reward would simply be delivered to them after the delay (Postponing Condition). The experiential task involved participants playing a video game that involved having to stop playing and wait for a larger number of points after a delay (Waiting Condition), or playing the game and getting the points delivered after the delay (Postponing Condition). We expected steeper discounting rates when waiting compared to postponing in both the experiential and hypothetical tasks. We found this effect only in the hypothetical task; however, this might be due to our procedure. We randomised the waiting and postponing trials in both tasks and this may have resulted in the participants being unable to discriminate between the interspersed trials. Experiment 2 investigated whether this methodological feature affected discounting in the experiential task, and we found that blocking the trials resulted in the anticipated effect. We found steeper discounting in both the experiential and hypothetical tasks for waiting compared to postponing after implementing this change, suggesting that waiting and postponing are different constructs. Experiment 3 investigated what drives the difference between waiting and postponing. We found that waiting has a greater effect on reward value than postponing due to the inability to access alternative reinforcement during the delay. We also investigated the relationships among our discounting measures and a measure of the consideration of future consequences, and a measure of delayed gratification. We found no correlation among discounting and these measures, and no consistent correlation between waiting and postponing. Overall, our results indicated that waiting and postponing are distinct constructs, and that the inability to access alternative reinforcement during a delay is the key difference between them.</p>

The Impact of Experiencing Outcomes on Delay and Probability Discounting

<p>Temporal and probability discounting refer to the decrease in subjective value of rewards that are either delayed or uncertain. Comparatively high degrees of discounting have been linked to other indices of impulsivity in both animals and humans, but the study of human discounting has primarily relied on participant reports of preferences between hypothetical outcomes. A number studies to date have illustrated not only how sensitive these preferences are to manipulations within such hypothetical procedures, but also that tasks where each consequence is actually experienced are able to capture changes in behaviour that hypothetical tasks may not. The current thesis examined temporal and probability discounting using a novel experiential discounting task in the form of a computer game-based discounting task in which the delays or probabilities of the preferred outcomes were experienced following each choice. The game had participants collect points by skiing over jumps, and discounting choices between either immediate and delayed or certain and uncertain point outcomes provided additional opportunities for point gain. Discounting was examined across four samples primarily composed of university students. Experiment 1, a test of the newly created task in two parts, assessed the most appropriate descriptive model of both temporal and probability discounting, as well as examined the relation between the two, hypothetical discounting and self-report measures of impulsivity and risk taking. Experiment 2 examined the effect of magnitude manipulations on both temporal and probability discounting. Experiment 3 examined the effect on degree of temporal discounting of manipulations to post-reward delays and access to alternative reinforcement during this period. Lastly, Experiment 4 attempted to manipulate the association between delay and risk and examined the impact of this on discounting of delayed outcomes. Participants across all studies showed systematic decreases in subjective value of both delayed and uncertain point outcomes. However, the shape of this decrease in value differed across the two types of outcomes, as did the effect of the magnitude manipulations. Furthermore, neither post-reinforcement duration, access to alternative reinforcement, nor experience with risk influenced degree of temporal discounting. The results are discussed in terms of single process accounts of discounting, the implications for individual trait interpretations of discounting and the relevance of experiential and hypothetical discounting to the construct of impulsivity.</p>

The Impact of Experiencing Outcomes on Delay and Probability Discounting

<p>Temporal and probability discounting refer to the decrease in subjective value of rewards that are either delayed or uncertain. Comparatively high degrees of discounting have been linked to other indices of impulsivity in both animals and humans, but the study of human discounting has primarily relied on participant reports of preferences between hypothetical outcomes. A number studies to date have illustrated not only how sensitive these preferences are to manipulations within such hypothetical procedures, but also that tasks where each consequence is actually experienced are able to capture changes in behaviour that hypothetical tasks may not. The current thesis examined temporal and probability discounting using a novel experiential discounting task in the form of a computer game-based discounting task in which the delays or probabilities of the preferred outcomes were experienced following each choice. The game had participants collect points by skiing over jumps, and discounting choices between either immediate and delayed or certain and uncertain point outcomes provided additional opportunities for point gain. Discounting was examined across four samples primarily composed of university students. Experiment 1, a test of the newly created task in two parts, assessed the most appropriate descriptive model of both temporal and probability discounting, as well as examined the relation between the two, hypothetical discounting and self-report measures of impulsivity and risk taking. Experiment 2 examined the effect of magnitude manipulations on both temporal and probability discounting. Experiment 3 examined the effect on degree of temporal discounting of manipulations to post-reward delays and access to alternative reinforcement during this period. Lastly, Experiment 4 attempted to manipulate the association between delay and risk and examined the impact of this on discounting of delayed outcomes. Participants across all studies showed systematic decreases in subjective value of both delayed and uncertain point outcomes. However, the shape of this decrease in value differed across the two types of outcomes, as did the effect of the magnitude manipulations. Furthermore, neither post-reinforcement duration, access to alternative reinforcement, nor experience with risk influenced degree of temporal discounting. The results are discussed in terms of single process accounts of discounting, the implications for individual trait interpretations of discounting and the relevance of experiential and hypothetical discounting to the construct of impulsivity.</p>

Effect of surface modification on mechanical properties of filature silk waste and nanoclay filler-based polymer matrix composite

Natural fibers have been attracting researchers and engineers as an alternative reinforcement of synthetic fibers in polymer composites due to their low cost, availability from natural resources, satisfactory high modulus and tensile strength, and biodegradability. Filature silk waste (FSW) is the remnant part of the cocoons which is produced during the silk forming process. The current study focuses on the comparison of tensile properties between untreated filature silk waste reinforced epoxy-based composite (UTFSWREC), 2 wt% alkali-treated filature silk waste reinforced epoxy-based composites (TFSWREC) and 2 wt% alkali-treated filature silk waste reinforced epoxy nanocomposites (TFSWRENC). The tensile properties showed that Young’s modulus of composites increases with surface modification of fiber and further enhances with nanoclay filler. TFSWREC and TFSWRENC displayed a higher tensile modulus than UTFSWREC. Scanning Electron Microscopy (SEM) showed the removal of the sericin layer from the surface of fiber, which resulted in the separation of fibrils and further resulted in the enhancement of the mechanical properties. FTIR analysis confirmed that intermolecular bonding improves with the chemical treatment and further refined with nanoclay filler addition.

ANALISA STABILITAS LERENG DAN ALTERNATIF PERKUATAN TANAH PADA JALUR KERETA API CEPAT JAKARTA-BANDUNG MENGGUNAKAN APLIKASI PLAXIS 8.6

Abstrak: Masalah dalam perencanaan struktur jalan kereta seperti tinggi lereng embankment yang lebih dari sama dengan 6 m, tanah asli yang tergolong sedang lunak, dan merupakan daerah rawan terjadinya longsor merupakan alasan dilakukannya penelitian ini. Hal tersebut didukung oleh hasil uji lab tanah, kondisi geografis dan geologis Kabupaten Purwakarta berupa bukit dan lembah yang terbentuk dari endapan batuan sedimen dan aluvium vulkanik dengan kemiringan lahan 8-40%. Oleh karena itu penelitian ini bertujuan untuk mengetahui stabilitas lereng embankment berupa nilai safety factor pada jalur kereta cepat Jakarta-Bandung daerah konstruksi DK70+150.00 sampai DK70+181.88. Adapun analisis numerik yang dilakukan pada penelitian ini menggunakan program Plaxis 8.6 yang dikembangkan berdasarkan metode Finite Element dengan model Mohr-Coulomb. Proses analisis dengan menginput parameter material yang dibutuhkan berdasarkan Mohr-Coulomb. Hasil analisis berupa angka safety factor yang menunjukkan kondisi stabilitas suatu lereng embankment. Penambahan alternatif perkuatan lereng embankment berupa cerucuk (micropile), bronjong (gabion) dan geotextile sebagai upaya pencegahan adanya kelongsoran jangka pendek dan panjang pada lereng embankment yang tidak stabil. Hasil analisis lereng embankment kereta api cepat Jakarta-Bandung DK70+150 sampai DK70+181.88 kondisi eksisting sebesar ΣMSF 1,1565 (cek global) dan ΣMSF 1,0515 (cek dinamik gempa) yang artinya lereng dalam kondisi tidak stabil dan perlu penambahan alternatif perkuatan. Berdasarkan simulasi kombinasi alternatif perkuatan. Menunjukkan kombinasi alternatif perkuatan geotextile dengan micropile menghasilkan angka safety factor ΣMSF 1,8151 (cek stabilitas global) dan ΣMSF 1,6262 (cek stabilitas akibat beban dinamik gempa).Kata-kata kunci: stabilitas lereng embankment, Plaxis 8.6, safety factor, kereta cepat Jakarta-BandungAbstract: Problems in the design of the railway structure such as the embankment slope height of 6 m, the original soil which is classified as moderately soft, and is an area prone to landslides is the reason for conducting this research. This is supported by the results of soil lab tests, geographical and geological conditions of Purwakarta Regency in the form of hills and valleys formed from sedimentary rock deposits and volcanic alluvium with a slope of 8-40%. Therefore, this study aims to determine the stability of the embankment slope in the form of the safety factor value on the Jakarta-Bandung high-speed rail line in the construction area DK70+150.00 to DK70+181.88. The numerical analysis carried out in this study used the Plaxis 8.6 program which was developed based on the Finite Element method with the Mohr-Coulomb model. The analysis process by inputting the required material parameters based on Mohr-Coulomb. The results of the analysis are in the form of safety factor numbers which indicate the stability condition of an embankment slope. The addition of alternative reinforcement for embankment slopes in the form of micropile, gabion (gabion) and geotextile as an effort to prevent short and long term landslides on unstable embankment slopes. The results of the slope analysis of the Jakarta-Bandung high-speed rail embankment DK70+150 to DK70+181.88 existing conditions of MSF: 1.1565 (global check) and MSF: 1.0515 (earthquake dynamics check) which means the slope is in an unstable condition and needs additional alternative reinforcement. Based on the simulation of alternative reinforcement combinations. Showing the alternative combination of geotextile reinforcement with micropile produces a safety factor number MSF: 1.8151 (check global stability) and MSF: 1.6262 (check stability due to dynamic earthquake loads)..Keywords: embankment slope stability, Plaxis 8.6, safety factor, Jakarta-Bandung high-speed train

Addiction as a brain disease revised: why it still matters, and the need for consilience

The view that substance addiction is a brain disease, although widely accepted in the neuroscience community, has become subject to acerbic criticism in recent years. These criticisms state that the brain disease view is deterministic, fails to account for heterogeneity in remission and recovery, places too much emphasis on a compulsive dimension of addiction, and that a specific neural signature of addiction has not been identified. We acknowledge that some of these criticisms have merit, but assert that the foundational premise that addiction has a neurobiological basis is fundamentally sound. We also emphasize that denying that addiction is a brain disease is a harmful standpoint since it contributes to reducing access to healthcare and treatment, the consequences of which are catastrophic. Here, we therefore address these criticisms, and in doing so provide a contemporary update of the brain disease view of addiction. We provide arguments to support this view, discuss why apparently spontaneous remission does not negate it, and how seemingly compulsive behaviors can co-exist with the sensitivity to alternative reinforcement in addiction. Most importantly, we argue that the brain is the biological substrate from which both addiction and the capacity for behavior change arise, arguing for an intensified neuroscientific study of recovery. More broadly, we propose that these disagreements reveal the need for multidisciplinary research that integrates neuroscientific, behavioral, clinical, and sociocultural perspectives.